I've gotten back around to trying out Google App Engine.
The main area that I have heard about it has been in my dealings with Grails, but I am sticking with the plain Java capabilities for my initial experimenting.
It seems fairly trivial to build and deploy some servlets using the Google plugin for Eclipse - even though that has meant switching back to a Ganymede version of Eclipse instead of the shiney new Galileo.
Being the curious sort, the first chunk of original-ish code that I deployed within my application was a servlet that iterates over the System properties of the server that is running the application and outputs them to the response.
After some sleep I think I will have a go at implementing a distributed game of noughts and crosses using AJAX and some servlets. This seems like it should be a simple enough game to implement, but will have the challenges of keeping track of players and game state.