Initially, I wasn't impressed by Google's cloud offering. It seemed restrictive compared to EC2 and I didn't feel like wasting time to convert my code to a new programming language. The engineering team behind GAE continued to improve the service and eventually, with the release of the Java early preview, I was sold. In fact I am considering using GAE exclusively for my future projects.

Nitro, my lightweight JSGI Web Application Framework runs great on App Engine, thanks to Rhino. Moreover, I am working on appengine, a ServerJS package that exposes the GAE Java APIs to JavaScript. The project is in its infancy but I just added the beginnings of a port of the Python ext.db API. I think it is more intuitive than the JDO/JPA APIs. You can find an early version here. Hopefully, this code will attract some contributors to help with implementing more advanced features like GqlQuery.

Update: The name of the project was changed to 'appengineJS'.