LGTM, although I wonder how much effect it has on build time. I can't imagine anyone ever wanting crappier icons, but if it say, doubled build time, we can always add an option like <set-configuration-property name="imageBundle.draftQuality" value="true"/> or something.
http://gwt-code-reviews.appspot.com/1663803/ -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
