I'd like to ask you about your experiences in developing facebook applications in Python. Which of the popular web frameworks for this language you think best suits this purpose? I know "best" is a very subjective word, so I'm specifically interested in the following:

Most reusable libraries. For example one might want to automatically create accounts for new logged in facebook users, but at the same time provide an alternative username + password logging functionality. I need authentication to fit into this nicely.
Facebook applications tend to differ from CMS-like sites. They are action intensive. For more complicated use-cases, usually some kind of caching for the data fetched from Open Graph API is required in order to be able to perform some queries on local and facebook data at once (for example join some tables based on friendship relation).
I'd definitely prefer popular solutions. They just seem to be much more stable and better thought through. I've previously developed a facebook application in Grails and I as much as I liked the architecture and the general ideas, the amount of bugs and complication that I ran into was just a little bit too much. Also Groovy is still quite an exotic language to develop in, and this time I'm not going to work on my own.

I'm not new to Python, but definitely new to web development in Python. Though after the experience with Grails and all its twists and turns I doubt Python could really scare me.
If you do not want to start on Django now. Try learning Flask(which is comparatively a lot easier to begin than Django) and then start building app with Flask.
Python frameworks for developing facebook apps