A quick googling shows a nice blog post by the GWT team.
I can’t say anything about GWT-Ext, but the same basic methods will work regardless of technology.
Another feature for GWT that is suitable for a future release is runAsync. Check out the GWT Web Toolkit Contributors mailing list for several different posts on this topic, including this one . Basically, this will allow you to split your web application into several independent “sections” and download them on request.