Actually, I was considering using GWT over the AppEngine. It provides a lot of supported functionality (such as fast Image serving, OAuth & OpenID, BLOBStore, Memcache) that seem a bit of a pain to integrate with ROR. Those features in conjunction with the free quota limitations (for approximately 5 million page views per month) make it seem like an ideal low investment platform that can scale one demand. I'm just wondering if anyone chose ROR/Django over GAE and what their reasoning might be.