The implementation seems fine. Could you also create a bug in the external GWT issue tracker and add it to the CL description, so we can track when this gets into a stable release?
Also, for those coming in late, please add a bit of justification to the issue. All our existing widgets are getting along fine by without this. I'm assuming it's because they know which elements are in the set and can use the isSelected() method as a filter, or something like that. So when does this functionality come in handy? http://gwt-code-reviews.appspot.com/1798806/ -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
