GWT 2.1 includes an MVP framework which includes an implementation of the PlaceService outlined by Google's Ray Ryan at Google I/O 2009.
That talk inspired some MVP frameworks like
Does GWT 2.1 make using these additional frameworks redundant?
Yes, there is overlap, and perhaps those other frameworks will become unnecessary down the road. But, from a practical perspective, to date there don't seem to be too many solid examples that use the new 2.1 features. On my current project we spent a little time evaluating the 2.1 MVP constructs and settled on using the GWT-presenter framework because we were able to make progress a lot faster using examples such as the Hupa mail client.
Unfortunately, all of these frameworks seem to lack solid documentation. They all seem to give you a trivial Hello World example, without showing you the essential details necessary to do anything more than a trivial example. The only way to learn is to dig through code.