Some cool new features were released yesterday for App Engine. :
Incoming Email - You can now enable mail as an inbound service (just like XMPP) so users can email your application at email@example.com. Inbound messages are converted to HTTP requests (just like XMPP) which you can receive via webhook handler.
Delete an App - Finally you are now able to delete an app! This has been one of the top 5 most requested features on the issue tracker. I have a bunch of old apps that I need to delete from when I first started groking App Engine. One thing to note when deleting an app - the appid can never be reused after deletion.
Datastore Stats - You can now see more detailed statistics about how your application data is stored in the Admin Console and also programmatically.