I've recently come across GWT (Google Web Toolkit) and have been amazed by it. I was wondering if anyone has ever put it to use making a video game? And if they did, what their experience was, whether it was worth it and whether the game was any good.
You might be interested in a talk from this year's Google I/O about using GWT, WebGL, and App Engine to build game tools. I would never have imagined that could be a really killer combination but was really surprised at how awesome it looked.
In addition to the EA game mentioned in amitp's comment, Rovio used GWT to port "Angry Birds" to the web (with a bit of Flash to work around HTML5's sad audio situation).