I've run a few small side projects on GAE (Google App Engine). I use it as a very simple and fast way to get an MVP off. My major issue is that their documentation tends to lag (sometimes way behind) when they change stuff, especially things that are integrated to other services they provide. For example after dropping support for OpenID 2.0, the documentation for 'Authentication Type' on Google App Engine was not updated to reflect this, neither was the documentation for securing your urls. This cost me considerable time and effort.
I'm a Product Manager on App Engine and I truly apologize for the trouble you went through when you tried the platform. We have kicked off a large initiative to update and enhance our docs, and we just recently launched our new App Engine docs, an ongoing project of course. You can check them out here:
Please give the new set of docs a try and please give us feedback when you see errors or generally when the content is not up to par with what you expect. There is a tool on the top right hand side of every page that explains this.
