Developping on top of Facebook Platform is very unsettling : always moving, inconsistent, under-documented, poor libraries outside of python and PHP, at least 3 types of access to the same data (deprecated REST API, FQL queries and Graph API), etc.
Yet you get their gigantic audience and unprecedented data at hand, which is thrilling.
Developping for Facebook is almost a separate kind of programing, with its own set of rules.