During last year, I wrote a couple of Facebook apps.
I used both, the beloved (by Facebook) PHP library for that and the Python library, and (not) surprisingly I found that writing Facebook apps on Python (and mostly because you have the handy AppEngine for deploying those) is way easier and needs no special treatment from your customers (you handle them the code and access to the application panel).
So along with my projects I used mostly the same approach, ending up with the code I published today on github.
This is a simple MVC like framework, which I recommend checking out to anyone who wants to try writing the Facebook apps on Google’s AppEngine.