YUI's base and fonts. Their reset is already in compass core.

Grid is still to come -- I'm still getting my head around its semantics.

examples/yui_default/stylesheets/screen.sass

@@ -0,0 +1,14 @@
+@import yui/screen
+@import compass/reset
+
+html
+  +reset-html
+
+body
+  +yui
+
+#my-small-element
+  +yui-font-size(10px)
+
+#my-big-element
+  +yui-font-size(24px)

frameworks/yui/stylesheets/yui/_screen.sass

@@ -0,0 +1,5 @@
+@import modules/base
+@import modules/fonts
+=yui
+  +yui-base
+  +yui-fonts

frameworks/yui/stylesheets/yui/modules/_base.sass

@@ -0,0 +1,60 @@
+=yui-base
+  h1
+    :font-size 138.5%
+
+  h2
+    :font-size 123.1%
+
+  h3
+    :font-size 108%
+
+  h1, h2, h3
+    :margin 1em 0
+
+  h1,h2, h3, h4, h5, h6, strong
+    :font-weight bold
+
+  abbr, acronym
+    :border-bottom 1px dotted #000
+    :cursor help
+
+  em
+    :font-style italic
+
+  blockquote
+    :margin 1em
+
+  ul
+    :margin 1em
+    :margin-left 2em
+    li
+      :list-style disc outside
+
+  ol
+    :margin 1em
+    :margin-left 2em
+    li
+      :list-style decimal outside
+
+  dl
+    :margin 1em
+    :margin-left 2em
+    dd
+      :margin-left 1em
+
+  th
+    :border 1px solid #000
+    :padding .5em
+    :font-weight bold
+    :text-align center
+
+  td
+    :border 1px solid #000
+    :padding .5em
+
+  caption
+    :margin-bottom .5em
+    :text-align center
+
+  p, fieldset, table
+    :margin-bottom 1em

frameworks/yui/stylesheets/yui/modules/_fonts.sass

@@ -0,0 +1,52 @@
+// Converts pixels to percents according to 
+// the table found at http://developer.yahoo.com/yui/fonts/#fontsize
+=yui-font-size(!size)
+  @if !size == 10px
+    :font-size 77%
+  @if !size == 11px
+    :font-size 85%
+  @if !size == 12px
+    :font-size 93%
+  @if !size == 13px
+    :font-size 100%
+  @if !size == 14px
+    :font-size 108%
+  @if !size == 15px
+    :font-size 116%
+  @if !size == 16px
+    :font-size 123.1%
+  @if !size == 17px
+    :font-size 131%
+  @if !size == 18px
+    :font-size 138.5%
+  @if !size == 19px
+    :font-size 146.5%
+  @if !size == 20px
+    :font-size 153.9%
+  @if !size == 21px
+    :font-size 161.6%
+  @if !size == 22px
+    :font-size 167%
+  @if !size == 23px
+    :font-size 174%
+  @if !size == 24px
+    :font-size 182%
+  @if !size == 25px
+    :font-size 189%
+  @if !size == 26px
+    :font-size 197%
+
+=yui-fonts
+  body
+    :font 13px/1.231 arial,helvetica,clean,sans-serif
+    :*font-size small
+    :*font x-small
+
+  table
+    :font-size inherit
+    :font 100%
+
+  pre, code, kbd, samp, tt
+    :font-family monospace
+    :*font-size 108%
+    :line-height 100%

frameworks/yui/templates/project/screen.sass

@@ -0,0 +1,8 @@
+@import yui/screen
+@import compass/reset
+
+html
+  +reset-html
+
+body
+  +yui

lib/compass/frameworks.rb

@@ -24,3 +24,4 @@ end
 
 require File.join(File.dirname(__FILE__), 'frameworks', 'compass')
 require File.join(File.dirname(__FILE__), 'frameworks', 'blueprint')
+require File.join(File.dirname(__FILE__), 'frameworks', 'yui')

lib/compass/frameworks/yui.rb

@@ -0,0 +1,2 @@
+yui_dir = File.join(Compass.base_directory, 'frameworks', 'yui')
+Compass::Frameworks.register('yui', yui_dir)