diff --git a/examples/demo.rb b/examples/demo.rb
index a777862..3f8fb12 100644
--- a/examples/demo.rb
+++ b/examples/demo.rb
@@ -16,5 +16,5 @@ coll.insert(doc)
 doc = {'a' => 3}
 coll.insert(doc)
 
-puts coll.count()
+puts "There are #{coll.count()} records in the test collection. Here they are:"
 coll.find().each { |doc| puts doc.inspect }
diff --git a/lib/mongo.rb b/lib/mongo.rb
index a35e535..6b300b4 100644
--- a/lib/mongo.rb
+++ b/lib/mongo.rb
@@ -1,4 +1,5 @@
 require 'mongo/mongo'
+require 'mongo/objectid'
 require 'mongo/message'
 require 'mongo/db'
 require 'mongo/cursor'
diff --git a/lib/mongo/objectid.rb b/lib/mongo/objectid.rb
new file mode 100644
index 0000000..bdbf310
--- /dev/null
+++ b/lib/mongo/objectid.rb
@@ -0,0 +1,37 @@
+# Copyright (C) 2008 10gen Inc.
+#
+# This program is free software: you can redistribute it and/or modify it
+# under the terms of the GNU Affero General Public License, version 3, as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License
+# for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+require 'mongo/util/uuid'
+
+module XGen
+  module Mongo
+    module Driver
+
+      class ObjectID
+
+        # String UUID
+        attr_reader :uuid
+
+        # uuid is a string
+        def initialize(uuid=nil)
+          @uuid ||= UUID.new.generate
+        end
+
+        def to_s
+          @uuid
+        end
+      end
+    end
+  end
+end
diff --git a/lib/mongo/query.rb b/lib/mongo/query.rb
index 259e762..e95ab23 100644
--- a/lib/mongo/query.rb
+++ b/lib/mongo/query.rb
@@ -32,7 +32,7 @@ module XGen
         end
 
         def selector=(sel)
-          @selector = case selector
+          @selector = case sel
                       when nil
                         {}
                       when String
diff --git a/lib/mongo/util/bson.rb b/lib/mongo/util/bson.rb
index 84ffbe6..07d2bed 100644
--- a/lib/mongo/util/bson.rb
+++ b/lib/mongo/util/bson.rb
@@ -1,4 +1,5 @@
 require 'mongo/util/byte_buffer'
+require 'mongo/objectid'
 
 class BSON
 
@@ -152,7 +153,7 @@ class BSON
   end
 
   def deserialize_oid_data
-    ObjectID.new(buf.get(12).pack("C*"))
+    XGen::Mongo::Driver::ObjectID.new(buf.get(12).pack("C*"))
   end
 
   def serialize_eoo_element(buf)
@@ -189,7 +190,7 @@ class BSON
   def serialize_object_element(buf, key, val)
     buf.put(OBJECT)
     self.class.serialize_cstr(buf, key)
-    BSON.new(buf).serialize(val)
+    buf.put_array(BSON.new.serialize(val).to_a)
   end
 
   def serialize_oid_element(buf, key, val)
@@ -241,7 +242,7 @@ class BSON
       key == "$where" ? CODE : STRING
     when Array
       ARRAY
-    when ObjectID
+    when XGen::Mongo::Driver::ObjectID
       OID
     when true, false
       Boolean
diff --git a/lib/mongo/util/macaddr.rb b/lib/mongo/util/macaddr.rb
new file mode 100644
index 0000000..11a0fcd
--- /dev/null
+++ b/lib/mongo/util/macaddr.rb
@@ -0,0 +1,71 @@
+# http://codeforpeople.com/lib/ruby/macaddr/macaddr-1.0.0/lib/macaddr.rb
+#
+##
+# Cross platform MAC address determination.  Works for:
+# * /sbin/ifconfig
+# * /bin/ifconfig
+# * ifconfig
+# * ipconfig /all
+#
+# To return the first MAC address on the system:
+#
+#   Mac.address
+#
+# To return an array of all MAC addresses:
+#
+#   Mac.address.list
+
+module Mac
+  VERSION = '1.0.0'
+
+  def Mac.version() ::Mac::VERSION end
+
+  class << self
+
+    ##
+    # Accessor for the system's first MAC address, requires a call to #address
+    # first
+
+    attr_accessor "mac_address"
+
+    ##
+    # Discovers and returns the system's MAC addresses.  Returns the first
+    # MAC address, and includes an accessor #list for the remaining addresses:
+    #
+    #   Mac.addr # => first address
+    #   Mac.addr.list # => all addresses
+
+    def address
+      return @mac_address if defined? @mac_address and @mac_address
+      re = %r/[^:\-](?:[0-9A-F][0-9A-F][:\-]){5}[0-9A-F][0-9A-F][^:\-]/io
+      cmds = '/sbin/ifconfig', '/bin/ifconfig', 'ifconfig', 'ipconfig /all'
+
+      null = test(?e, '/dev/null') ? '/dev/null' : 'NUL'
+
+      lines = nil
+      cmds.each do |cmd|
+        stdout = IO.popen("#{ cmd } 2> #{ null }"){|fd| fd.readlines} rescue next
+        next unless stdout and stdout.size > 0
+        lines = stdout and break
+      end
+      raise "all of #{ cmds.join ' ' } failed" unless lines
+
+      candidates = lines.select{|line| line =~ re}
+      raise 'no mac address candidates' unless candidates.first
+      candidates.map!{|c| c[re].strip}
+
+      maddr = candidates.first
+      raise 'no mac address found' unless maddr
+
+      maddr.strip!
+      maddr.instance_eval{ @list = candidates; def list() @list end }
+
+      @mac_address = maddr
+    end
+
+    ##
+    # Shorter alias for #address
+
+    alias_method "addr", "address"
+  end
+end
diff --git a/lib/mongo/util/uuid.rb b/lib/mongo/util/uuid.rb
new file mode 100644
index 0000000..e170643
--- /dev/null
+++ b/lib/mongo/util/uuid.rb
@@ -0,0 +1,281 @@
+#
+# = uuid.rb - UUID generator
+#
+# Author:: Assaf Arkin  assaf@labnotes.org
+#          Eric Hodel drbrain@segment7.net
+# Copyright:: Copyright (c) 2005-2008 Assaf Arkin, Eric Hodel
+# License:: MIT and/or Creative Commons Attribution-ShareAlike
+
+require 'fileutils'
+require 'thread'
+require 'tmpdir'
+
+# require 'rubygems'
+require 'mongo/util/macaddr'
+
+
+##
+# = Generating UUIDs
+#
+# Call #generate to generate a new UUID. The method returns a string in one of
+# three formats. The default format is 36 characters long, and contains the 32
+# hexadecimal octets and hyphens separating the various value parts. The
+# <tt>:compact</tt> format omits the hyphens, while the <tt>:urn</tt> format
+# adds the <tt>:urn:uuid</tt> prefix.
+#
+# For example:
+#
+#   uuid = UUID.new
+#   
+#   10.times do
+#     p uuid.generate
+#   end
+#
+# = UUIDs in Brief
+#
+# UUID (universally unique identifier) are guaranteed to be unique across time
+# and space.
+#
+# A UUID is 128 bit long, and consists of a 60-bit time value, a 16-bit
+# sequence number and a 48-bit node identifier.
+#
+# The time value is taken from the system clock, and is monotonically
+# incrementing.  However, since it is possible to set the system clock
+# backward, a sequence number is added.  The sequence number is incremented
+# each time the UUID generator is started.  The combination guarantees that
+# identifiers created on the same machine are unique with a high degree of
+# probability.
+#
+# Note that due to the structure of the UUID and the use of sequence number,
+# there is no guarantee that UUID values themselves are monotonically
+# incrementing.  The UUID value cannot itself be used to sort based on order
+# of creation.
+#
+# To guarantee that UUIDs are unique across all machines in the network,
+# the IEEE 802 MAC address of the machine's network interface card is used as
+# the node identifier.
+#
+# For more information see {RFC 4122}[http://www.ietf.org/rfc/rfc4122.txt].
+
+class UUID
+
+  VERSION = '2.0.1'
+
+  ##
+  # Clock multiplier. Converts Time (resolution: seconds) to UUID clock
+  # (resolution: 10ns)
+  CLOCK_MULTIPLIER = 10000000
+
+  ##
+  # Clock gap is the number of ticks (resolution: 10ns) between two Ruby Time
+  # ticks.
+  CLOCK_GAPS = 100000
+
+  ##
+  # Version number stamped into the UUID to identify it as time-based.
+  VERSION_CLOCK = 0x0100
+
+  ##
+  # Formats supported by the UUID generator.
+  #
+  # <tt>:default</tt>:: Produces 36 characters, including hyphens separating
+  #                     the UUID value parts
+  # <tt>:compact</tt>:: Produces a 32 digits (hexadecimal) value with no
+  #                     hyphens
+  # <tt>:urn</tt>:: Adds the prefix <tt>urn:uuid:</tt> to the default format
+  FORMATS = {
+    :compact => '%08x%04x%04x%04x%012x',
+    :default => '%08x-%04x-%04x-%04x-%012x',
+    :urn     => 'urn:uuid:%08x-%04x-%04x-%04x-%012x',
+  }
+
+  ##
+  # MAC address (48 bits), sequence number and last clock
+  STATE_FILE_FORMAT = 'SLLQ'
+
+  @state_file = nil
+  @mode = nil
+  @uuid = nil
+
+  ##
+  # The access mode of the state file.  Set it with state_file.
+
+  def self.mode
+    @mode
+  end
+
+  ##
+  # Generates a new UUID string using +format+.  See FORMATS for a list of
+  # supported formats.
+
+  def self.generate(format = :default)
+    @uuid ||= new
+    @uuid.generate format
+  end
+
+  ##
+  # Creates an empty state file in /var/tmp/ruby-uuid or the windows common
+  # application data directory using mode 0644.  Call with a different mode
+  # before creating a UUID generator if you want to open access beyond your
+  # user by default.
+  #
+  # If the default state dir is not writable, UUID falls back to ~/.ruby-uuid.
+  #
+  # State files are not portable across machines.
+  def self.state_file(mode = 0644)
+    return @state_file if @state_file
+
+    @mode = mode
+
+    begin
+      require 'Win32API'
+
+      csidl_common_appdata = 0x0023
+      path = 0.chr * 260
+      get_folder_path = Win32API.new('shell32', 'SHGetFolderPath', 'LLLLP', 'L')
+      get_folder_path.call 0, csidl_common_appdata, 0, 1, path
+
+      state_dir = File.join(path.strip)
+    rescue LoadError
+      state_dir = File.join('', 'var', 'tmp')
+    end
+
+    if File.writable?(state_dir) then
+      @state_file = File.join(state_dir, 'ruby-uuid')
+    else
+      @state_file = File.expand_path(File.join('~', '.ruby-uuid'))
+    end
+
+    @state_file
+  end
+
+  ##
+  # Create a new UUID generator.  You really only need to do this once.
+  def initialize
+    @drift = 0
+    @last_clock = (Time.now.to_f * CLOCK_MULTIPLIER).to_i
+    @mutex = Mutex.new
+
+    if File.exist?(self.class.state_file) then
+      next_sequence
+    else
+      @mac = Mac.addr.gsub(/:|-/, '').hex & 0x7FFFFFFFFFFF
+      fail "Cannot determine MAC address from any available interface, tried with #{Mac.addr}" if @mac == 0
+      @sequence = rand 0x10000
+
+      open_lock 'w' do |io|
+        write_state io
+      end
+    end
+  end
+
+  ##
+  # Generates a new UUID string using +format+.  See FORMATS for a list of
+  # supported formats.
+  def generate(format = :default)
+    template = FORMATS[format]
+
+    raise ArgumentError, "invalid UUID format #{format.inspect}" unless template
+
+    # The clock must be monotonically increasing. The clock resolution is at
+    # best 100 ns (UUID spec), but practically may be lower (on my setup,
+    # around 1ms). If this method is called too fast, we don't have a
+    # monotonically increasing clock, so the solution is to just wait.
+    #
+    # It is possible for the clock to be adjusted backwards, in which case we
+    # would end up blocking for a long time. When backward clock is detected,
+    # we prevent duplicates by asking for a new sequence number and continue
+    # with the new clock.
+
+    clock = @mutex.synchronize do
+      clock = (Time.new.to_f * CLOCK_MULTIPLIER).to_i & 0xFFFFFFFFFFFFFFF0
+
+      if clock > @last_clock then
+        @drift = 0
+        @last_clock = clock
+      elsif clock == @last_clock then
+        drift = @drift += 1
+
+        if drift < 10000 then
+          @last_clock += 1
+        else
+          Thread.pass
+          nil
+        end
+      else
+        next_sequence
+        @last_clock = clock
+      end
+    end until clock
+
+    template % [
+        clock        & 0xFFFFFFFF,
+       (clock >> 32) & 0xFFFF,
+      ((clock >> 48) & 0xFFFF | VERSION_CLOCK),
+      @sequence      & 0xFFFF,
+      @mac           & 0xFFFFFFFFFFFF
+    ]
+  end
+
+  ##
+  # Updates the state file with a new sequence number.
+  def next_sequence
+    open_lock 'r+' do |io|
+      @mac, @sequence, @last_clock = read_state(io)
+
+      io.rewind
+      io.truncate 0
+
+      @sequence += 1
+
+      write_state io
+    end
+  rescue Errno::ENOENT
+    open_lock 'w' do |io|
+      write_state io
+    end
+  ensure
+    @last_clock = (Time.now.to_f * CLOCK_MULTIPLIER).to_i
+    @drift = 0
+  end
+
+  def inspect
+    mac = ("%012x" % @mac).scan(/[0-9a-f]{2}/).join(':')
+    "MAC: #{mac}  Sequence: #{@sequence}"
+  end
+
+protected
+
+  ##
+  # Open the state file with an exclusive lock and access mode +mode+.
+  def open_lock(mode)
+    File.open self.class.state_file, mode, self.class.mode do |io|
+      begin
+        io.flock File::LOCK_EX
+        yield io
+      ensure
+        io.flock File::LOCK_UN
+      end
+    end
+  end
+
+  ##
+  # Read the state from +io+
+  def read_state(io)
+    mac1, mac2, seq, last_clock = io.read(32).unpack(STATE_FILE_FORMAT)
+    mac = (mac1 << 32) + mac2
+
+    return mac, seq, last_clock
+  end
+
+
+  ##
+  # Write that state to +io+
+  def write_state(io)
+    mac2 =  @mac        & 0xffffffff
+    mac1 = (@mac >> 32) & 0xffff
+
+    io.write [mac1, mac2, @sequence, @last_clock].pack(STATE_FILE_FORMAT)
+  end
+  
+end