diff --git a/Gemfile.lock b/Gemfile.lock
index 86c2008b..7d934b0f 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -7,8 +7,8 @@ GIT
 PATH
   remote: .
   specs:
-    compass (0.11.3.e4a22c4)
-      chunky_png (~> 1.1)
+    compass (0.11.3.a6a7069)
+      chunky_png (~> 1.2)
       fssm (>= 0.2.7)
       sass (~> 3.1)
 
diff --git a/compass.gemspec b/compass.gemspec
index 87e2436f..d6c1194e 100644
--- a/compass.gemspec
+++ b/compass.gemspec
@@ -16,7 +16,7 @@ Gem::Specification.new do |gemspec|
   gemspec.summary = %q{A Real Stylesheet Framework}
 
   gemspec.add_dependency 'sass', '~> 3.1'
-  gemspec.add_dependency 'chunky_png', '~> 1.1'
+  gemspec.add_dependency 'chunky_png', '~> 1.2'
   gemspec.add_dependency 'fssm', '>= 0.2.7'
 
   gemspec.files = %w(README.markdown LICENSE.markdown VERSION.yml Rakefile)
diff --git a/doc-src/content/help/tutorials/configuration-reference.markdown b/doc-src/content/help/tutorials/configuration-reference.markdown
index af6d6ea7..3a966856 100644
--- a/doc-src/content/help/tutorials/configuration-reference.markdown
+++ b/doc-src/content/help/tutorials/configuration-reference.markdown
@@ -308,9 +308,12 @@ the asset host configuration is ignored.
 ---
 
 **`asset_cache_buster`** – Pass this function a block of code that defines the
-cache buster strategy to be used. The block must return nil or a string that can
-be appended to a url as a query parameter. The returned string must not include
-the starting `?`. The block will be passed the root-relative url of the asset.
+cache buster strategy to be used. The block must return nil, a string or a hash.
+If the returned value is a hash the values of :path and/or :query is used to generate
+a cache busted path to the asset. If a string value is returned, it is added as a query string.
+The returned values for query strings must not include the starting `?`.
+
+The block will be passed the root-relative url of the asset.
 If the block accepts two arguments, it will also be passed a path
 that points to the asset on disk — which may or may not exist.
 
@@ -324,6 +327,18 @@ that points to the asset on disk — which may or may not exist.
       end
     end
 
+Busting the cache via path:
+
+    asset_cache_buster do |path, real_path|
+      if File.exists?(real_path)
+        pathname = Pathname.new(path)
+        modified_time = File.mtime(real_path).strftime("%s")
+        new_path = "%s/%s-%s%s" % [pathname.dirname, pathname.basename(pathname.extname), modified_time, pathname.extname]
+
+        {:path => new_path, :query => nil}
+      end
+    end
+
 To disable the asset cache buster:
 
     asset_cache_buster :none
diff --git a/features/command_line.feature b/features/command_line.feature
index f0be79b1..06e0060c 100644
--- a/features/command_line.feature
+++ b/features/command_line.feature
@@ -145,6 +145,7 @@ Feature: Command Line
   Scenario: Basic help
     When I run: compass help
     Then I should see the following "primary" commands:
+      | clean   |
       | compile |
       | create  |
       | init    |
@@ -179,6 +180,27 @@ Feature: Command Line
     And I run: compass compile
     And a css file tmp/layout.css is reported overwritten
 
+  Scenario: Cleaning a project
+    Given I am using the existing project in test/fixtures/stylesheets/compass
+    When I run: compass compile
+    And I run: compass clean
+    Then the following files are reported removed:
+      | .sass-cache/                |
+      | tmp/border_radius.css       |
+      | tmp/box.css                 |
+      | tmp/box_shadow.css          |
+      | tmp/columns.css             |
+      | tmp/fonts.css               |
+      | images/flag-s03c3b29b35.png |
+    And the following files are removed:
+      | .sass-cache/                |
+      | tmp/border_radius.css       |
+      | tmp/box.css                 |
+      | tmp/box_shadow.css          |
+      | tmp/columns.css             |
+      | tmp/fonts.css               |
+      | images/flag-s03c3b29b35.png |
+
   Scenario: Watching a project for changes
     Given ruby supports fork
     Given I am using the existing project in test/fixtures/stylesheets/compass
@@ -218,7 +240,6 @@ Feature: Command Line
       | sass_dir | sass       |
       | css_dir  | assets/css |
 
-  @now
   Scenario Outline: Print out a configuration value
     Given I am using the existing project in test/fixtures/stylesheets/compass
     When I run: compass config -p <property>
diff --git a/features/step_definitions/command_line_steps.rb b/features/step_definitions/command_line_steps.rb
index 8811693d..5bddd7a7 100644
--- a/features/step_definitions/command_line_steps.rb
+++ b/features/step_definitions/command_line_steps.rb
@@ -116,10 +116,30 @@ Then /^a directory ([^ ]+) is (not )?created$/ do |directory, negated|
   File.directory?(directory).should == !negated
 end
  
+Then /an? \w+ file ([^ ]+) is (not )?removed/ do |filename, negated|
+  File.exists?(filename).should == !!negated
+end
+
 Then /an? \w+ file ([^ ]+) is (not )?created/ do |filename, negated|
   File.exists?(filename).should == !negated
 end
 
+Then "the following files are reported removed:" do |table|
+  table.rows.each do |css_file|
+    Then %Q{a css file #{css_file.first} is reported removed}
+  end
+end
+
+Then "the following files are removed:" do |table|
+  table.rows.each do |css_file|
+    Then %Q{a css file #{css_file.first} is removed}
+  end
+end
+
+Then /an? \w+ file ([^ ]+) is reported removed/ do |filename|
+  @last_result.should =~ /remove.*#{Regexp.escape(filename)}/
+end
+
 Then /an? \w+ file ([^ ]+) is reported created/ do |filename|
   @last_result.should =~ /create.*#{Regexp.escape(filename)}/
 end
diff --git a/lib/compass/actions.rb b/lib/compass/actions.rb
index bc4a2b82..4e924f1b 100644
--- a/lib/compass/actions.rb
+++ b/lib/compass/actions.rb
@@ -65,7 +65,10 @@ module Compass
     end
 
     def remove(file_name)
-      if File.exists?(file_name)
+      if File.directory?(file_name)
+        FileUtils.rm_rf file_name
+        log_action :remove, basename(file_name)+"/", options
+      elsif File.exists?(file_name)
         File.unlink file_name
         log_action :remove, basename(file_name), options
       end
diff --git a/lib/compass/commands.rb b/lib/compass/commands.rb
index f4230ef4..42ca37ab 100644
--- a/lib/compass/commands.rb
+++ b/lib/compass/commands.rb
@@ -4,7 +4,7 @@ end
 require 'compass/commands/registry'
 
 %w(base generate_grid_background default help list_frameworks project_base
-   update_project watch_project create_project imports installer_command
+   update_project watch_project create_project clean_project imports installer_command
    print_version project_stats stamp_pattern sprite validate_project
    write_configuration interactive unpack_extension).each do |lib|
   require "compass/commands/#{lib}"
diff --git a/lib/compass/commands/clean_project.rb b/lib/compass/commands/clean_project.rb
new file mode 100644
index 00000000..e6792326
--- /dev/null
+++ b/lib/compass/commands/clean_project.rb
@@ -0,0 +1,79 @@
+require 'compass/commands/project_base'
+require 'compass/compiler'
+
+module Compass
+  module Commands
+    module CleanProjectOptionsParser
+      def set_options(opts)
+        opts.banner = %Q{
+          Usage: compass clean [path/to/project] [options]
+
+          Description:
+          Remove generated files and the sass cache.
+
+          Options:
+        }.split("\n").map{|l| l.gsub(/^ */,'')}.join("\n")
+
+        super
+      end
+    end
+
+    class CleanProject < UpdateProject
+
+      register :clean
+
+      def initialize(working_path, options)
+        super
+        assert_project_directory_exists!
+      end
+
+      def perform
+        compiler = new_compiler_instance
+        compiler.clean!
+        Compass::SpriteImporter.find_all_sprite_map_files(Compass.configuration.images_path).each do |sprite|
+          remove sprite
+        end
+      end
+
+      def determine_cache_location
+        Compass.configuration.cache_path || Sass::Plugin.options[:cache_location] || File.join(working_path, ".sass-cache")
+      end
+
+      class << self
+        def option_parser(arguments)
+          parser = Compass::Exec::CommandOptionParser.new(arguments)
+          parser.extend(Compass::Exec::GlobalOptionsParser)
+          parser.extend(Compass::Exec::ProjectOptionsParser)
+          parser.extend(CleanProjectOptionsParser)
+        end
+
+        def usage
+          option_parser([]).to_s
+        end
+
+        def primary; true; end
+
+        def description(command)
+          "Remove generated files and the sass cache"
+        end
+
+        def parse!(arguments)
+          parser = option_parser(arguments)
+          parser.parse!
+          parse_arguments!(parser, arguments)
+          parser.options
+        end
+
+        def parse_arguments!(parser, arguments)
+          if arguments.size > 0
+            parser.options[:project_name] = arguments.shift if File.directory?(arguments.first)
+            unless arguments.empty?
+              parser.options[:sass_files] = arguments.dup
+              parser.options[:force] = true
+            end
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/compass/commands/registry.rb b/lib/compass/commands/registry.rb
index 64372079..3b5c0d16 100644
--- a/lib/compass/commands/registry.rb
+++ b/lib/compass/commands/registry.rb
@@ -16,8 +16,10 @@ module Compass::Commands
         matching.first
       elsif name =~ /^-/
         nil
-      else
+      elsif matching.size > 1
         raise Compass::Error, "Ambiguous abbreviation '#{name}'. Did you mean one of: #{matching.join(", ")}"
+      else
+        raise Compass::Error, "Command not found: #{name}"
       end
     end
     def abbreviation?(name)
diff --git a/lib/compass/commands/update_project.rb b/lib/compass/commands/update_project.rb
index d570da2f..30e2654f 100644
--- a/lib/compass/commands/update_project.rb
+++ b/lib/compass/commands/update_project.rb
@@ -54,6 +54,7 @@ module Compass
           compiler_opts = {:sass => Compass.sass_engine_options}
           compiler_opts.merge!(options)
           compiler_opts[:sass_files] = explicit_sass_files
+          compiler_opts[:cache_location] = determine_cache_location
           compiler_opts
         end
 
diff --git a/lib/compass/compiler.rb b/lib/compass/compiler.rb
index 961a4624..606f9406 100644
--- a/lib/compass/compiler.rb
+++ b/lib/compass/compiler.rb
@@ -75,9 +75,9 @@ module Compass
     end
 
     def clean!
-      FileUtils.rm_rf options[:cache_location]
+      remove options[:cache_location]
       css_files.each do |css_file|
-        FileUtils.rm_f css_file
+        remove css_file
       end
     end
 
diff --git a/lib/compass/configuration/data.rb b/lib/compass/configuration/data.rb
index 9cde724d..ddc2de3a 100644
--- a/lib/compass/configuration/data.rb
+++ b/lib/compass/configuration/data.rb
@@ -71,8 +71,10 @@ module Compass
       end
 
       # When called with a block, defines the cache buster strategy to be used.
-      # The block must return nil or a string that can be appended to a url as a query parameter.
-      # The returned string must not include the starting '?'.
+      # If the block returns nil or a string, then it is appended to the url as a query parameter.
+      # In this case, the returned string must not include the starting '?'.
+      # The block may also return a hash with :path and/or :query values and it
+      # will replace the original path and query string with the busted values returned.
       # The block will be passed the root-relative url of the asset.
       # If the block accepts two arguments, it will also be passed a File object
       # that points to the asset on disk -- which may or may not exist.
diff --git a/lib/compass/exec/sub_command_ui.rb b/lib/compass/exec/sub_command_ui.rb
index 972f82c8..43a5a308 100644
--- a/lib/compass/exec/sub_command_ui.rb
+++ b/lib/compass/exec/sub_command_ui.rb
@@ -13,6 +13,7 @@ module Compass::Exec
     def run!
       begin
         perform!
+        return 0
       rescue Exception => e
         raise e if e.is_a? SystemExit
         if e.is_a?(::Compass::Error) || e.is_a?(OptionParser::ParseError)
@@ -22,7 +23,6 @@ module Compass::Exec
         end
         return 1
       end
-      return 0
     end
     
     protected
diff --git a/lib/compass/sass_extensions/functions/urls.rb b/lib/compass/sass_extensions/functions/urls.rb
index d140c8a5..50ffab52 100644
--- a/lib/compass/sass_extensions/functions/urls.rb
+++ b/lib/compass/sass_extensions/functions/urls.rb
@@ -91,9 +91,7 @@ module Compass::SassExtensions::Functions::Urls
       if cache_buster.is_a?(Sass::Script::String)
         path += "?#{cache_buster.value}"
       else
-        if buster = compute_cache_buster(path, real_path)
-          path += "?#{buster}"
-        end
+        path = cache_busted_path(path, real_path)
       end
     end
 
@@ -137,6 +135,23 @@ module Compass::SassExtensions::Functions::Urls
     end
   end
 
+  def cache_busted_path(path, real_path)
+    cache_buster = compute_cache_buster(path, real_path)
+    if cache_buster.nil?
+      return path
+    elsif cache_buster.is_a?(String)
+      cache_buster = {:query => cache_buster}
+    else
+      path = cache_buster[:path] if cache_buster[:path]
+    end
+    
+    if cache_buster[:query]
+      "%s?%s" % [path, cache_buster[:query]]
+    else
+      path
+    end
+  end
+
   def compute_cache_buster(path, real_path)
     if Compass.configuration.asset_cache_buster
       args = [path]
diff --git a/lib/compass/sprite_importer.rb b/lib/compass/sprite_importer.rb
index 459c20e6..3dd1bd3e 100644
--- a/lib/compass/sprite_importer.rb
+++ b/lib/compass/sprite_importer.rb
@@ -4,7 +4,14 @@ module Compass
     VAILD_FILE_NAME = /\A#{Sass::SCSS::RX::IDENT}\Z/
     SPRITE_IMPORTER_REGEX = %r{((.+/)?([^\*.]+))/(.+?)\.png}
     VALID_EXTENSIONS = ['.png']
-    
+
+    # finds all sprite files
+    def self.find_all_sprite_map_files(path)
+      hex = "[0-9a-f]"
+      glob = "*-{,s}#{hex*10}{#{VALID_EXTENSIONS.join(",")}}"
+      Dir.glob(File.join(path, "**", glob))
+    end
+
     def self.load(uri, options)
       klass = Compass::SpriteImporter.new
       klass.uri, klass.options = uri, options
diff --git a/test/fixtures/stylesheets/busted_image_urls/config.rb b/test/fixtures/stylesheets/busted_image_urls/config.rb
new file mode 100644
index 00000000..13821b8e
--- /dev/null
+++ b/test/fixtures/stylesheets/busted_image_urls/config.rb
@@ -0,0 +1,29 @@
+# Require any additional compass plugins here.
+project_type = :stand_alone
+css_dir = "tmp"
+sass_dir = "sass"
+images_dir = "images"
+output_style = :compact
+# To enable relative image paths using the images_url() function:
+# http_images_path = :relative
+http_images_path = "/images"
+line_comments = false
+
+asset_cache_buster do |path, file|
+  pathname = Pathname.new(path)
+  
+  case pathname.basename(pathname.extname).to_s
+  when "grid"
+    new_path = "%s/%s-BUSTED%s" % [pathname.dirname, pathname.basename(pathname.extname), pathname.extname]
+    {:path => new_path, :query => nil}
+  when "feed"
+    "query_string"
+  when "dk"
+    {:query => "query_string"}
+  end
+end
+
+
+asset_host do |path|
+  "http://assets%d.example.com" % (path.size % 4)
+end
diff --git a/test/fixtures/stylesheets/busted_image_urls/css/screen.css b/test/fixtures/stylesheets/busted_image_urls/css/screen.css
new file mode 100644
index 00000000..ab36dbc7
--- /dev/null
+++ b/test/fixtures/stylesheets/busted_image_urls/css/screen.css
@@ -0,0 +1,9 @@
+.showgrid { background-image: url('http://assets0.example.com/images/grid-BUSTED.png'); }
+
+.inlinegrid { background-image: url('data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACgAAAAUEAYAAACv1qP4AAAABmJLR0T///////8JWPfcAAAACXBIWXMAAABIAAAASABGyWs+AAAAZ0lEQVRYw+3QwQ2AIBAFUTEUwI3+uzN7gDscsIgxEuO8An52J11X73OudfxMraXkzHfO3Y98nQEhA0IGhAwIGRAyIGRAyICQASEDQgaEDAgZEDIgZEDIgJABoZzSGK3tPuN9ERFP7Nw4fg+c5g8V1wAAAABJRU5ErkJggg=='); }
+
+.no-buster { background-image: url('http://assets0.example.com/images/grid.png'); }
+
+.feed { background-image: url('http://assets0.example.com/images/feed.png?query_string'); }
+
+.dk { background-image: url('http://assets0.example.com/images/flags/dk.png?query_string'); }
diff --git a/test/fixtures/stylesheets/busted_image_urls/images/feed.png b/test/fixtures/stylesheets/busted_image_urls/images/feed.png
new file mode 100644
index 00000000..315c4f4f
Binary files /dev/null and b/test/fixtures/stylesheets/busted_image_urls/images/feed.png differ
diff --git a/test/fixtures/stylesheets/busted_image_urls/images/flags/dk.png b/test/fixtures/stylesheets/busted_image_urls/images/flags/dk.png
new file mode 100644
index 00000000..5f660619
Binary files /dev/null and b/test/fixtures/stylesheets/busted_image_urls/images/flags/dk.png differ
diff --git a/test/fixtures/stylesheets/busted_image_urls/images/grid.png b/test/fixtures/stylesheets/busted_image_urls/images/grid.png
new file mode 100644
index 00000000..76aaa851
Binary files /dev/null and b/test/fixtures/stylesheets/busted_image_urls/images/grid.png differ
diff --git a/test/fixtures/stylesheets/busted_image_urls/sass/screen.sass b/test/fixtures/stylesheets/busted_image_urls/sass/screen.sass
new file mode 100644
index 00000000..b469b120
--- /dev/null
+++ b/test/fixtures/stylesheets/busted_image_urls/sass/screen.sass
@@ -0,0 +1,14 @@
+.showgrid
+  background-image: image-url("grid.png")
+
+.inlinegrid
+  background-image: inline-image("grid.png")
+
+.no-buster
+  background-image: image-url("grid.png", $only-path: false, $cache-buster: false)
+
+.feed
+  background-image: image-url("feed.png")
+
+.dk
+  background-image: image-url("flags/dk.png")
\ No newline at end of file
diff --git a/test/integrations/compass_test.rb b/test/integrations/compass_test.rb
index c8f4f5f8..b505debb 100644
--- a/test/integrations/compass_test.rb
+++ b/test/integrations/compass_test.rb
@@ -73,6 +73,17 @@ class CompassTest < Test::Unit::TestCase
     end
   end
 
+  def test_busted_image_urls
+    within_project('busted_image_urls') do |proj|
+      each_css_file(proj.css_path) do |css_file|
+        assert_no_errors css_file, 'busted_image_urls'
+      end
+      each_sass_file do |sass_file|
+        assert_renders_correctly sass_file
+      end
+    end
+  end
+
   def test_image_urls
     within_project('image_urls') do |proj|
       each_css_file(proj.css_path) do |css_file|