Just a link post today since google started supporting Java for their app engine rather than just Python, this will very likely bring lots of developers on board by having Java for Google App Engine

http://code.google.com/appengine/ Google AppEngine
http://code.google.com/eclipse/ Eclipse Plugin
http://blog.springsource.com/2009/04/07/write-your-google-app-engine-applications-in-groovy/ App Engine in Groovy

Time to start writing some apps in it 🙂