I came up with a few more questions after posting this and discussing it a bit with a colleague:

The lack of community support: Maybe this is because the most suitable target products are very, very niched and something that (mainly) companies develop, without contributing to the community? I.e. regular client developers have no good reason to use GWT since it’s quite tedious and not very familiar to their regular development (HTML/Javascript)? Just a theory.
Perhaps it will pick up some speed with the release of GWT 2.0…

Also, the Google documents (e.g. the MVP architecture article, http://code.google.com/webtoolkit/doc/latest/tutorial/mvp-architecture.html) leave a lot to your imagination and creativity. The examples are rather incomplete and you’ll have to do a bit of hit-and-miss before finding out what to do…