I got my Google App Engine account. I haven't gotten too far yet, "Hello World", a few silly deployment things. I am curious to see how nice the web app framework is. I am really curious to mess around with BigTable and see if I can put it to any good kind of use.
So far I'd compare it to Heroku (Rails thing on AWS), but the web framework standard WSGI is interesting. People really enjoy programming in Rails- it's unlikely, but possible, that Google's framework will achieve that. Just about any normal sort of web app thing you want to do in Rails is already done for you- and often done in a way that is better than I'd be able to do it myself in a reasonable amount of time. [update- it looks like you can run Django on there, minus the relational stuff, of course]
I know Google hired Guido, but I think they would have hit a home run if they had used a Rails stack with this. Of course, the piece that is "missing" is the relational database. BigTable might be a decent replacement, but certainly would be a serious adaptation of ActiveRecord.
I was looking around to see if anyone had done a knockout port of ActiveRecord to use SimpleDB, since that is somewhat similar to what we are doing on my own current web application project. We have stepped away from the RDBMS and are going with MarkLogic. It's great for reads, but I am really worried that doing updates is going to kill us.
Anyway, it's an interesting road. I'm going to hack some Python tonight and get my app deployed. Hope you're having fun too!