Moving Targets
I thought that trying to keep up with Drupal development was bad. Constantly changing APIs, functions parameters reordered, but at least that was once or twice a year. Facebook is even worse!
I've recently written a facebook app, ShiftBuddies, for the company I work for, Computerminds, we had some nice functionality that would show different content on a user's profile block depending on whether you were the profile's owner, or a visitor.