At work we're using GWT for a couple of projects now but we have never used the MVP pattern recommended by Google. So to learn it i wrote a small application called Quake Statistics that uses the recomendations. The app pulls data from quakelive.com each night and can plot the it along with some very basic analysis.
It's actually motivation to see if you're getting better at the game. Of course this was also an excuse to get to play quakelive more, to test the stats :)
The application can be accessed at http://quakestatistics.appspot.com and if you want to play around with some example data you can try my profile. Since i don't have that many users the page can be a bit slow because AppEngine have to restart after 1 min idle time.
Yes, i know. The design desperately need some (a lot of) improvements but unfortunately i'm a programmer not a designer. Right now I am in the process of rewriting the app for GWT 2.0 so if you want to help with the design and/or have some suggestions don't hesitate to contact me.