It's the only reason I've ever been interested in Apple's mobile devices. I joined the iPhone Dev Team right after the iPhone came out and worked on it through the initial unlock. Once the challenge was gone, I moved on to greener pastures. It wasn't to get some specific goal (I never really installed any apps on my phone), but just to do it and have some fun. Everyone should reverse-engineer something like that at some point -- the feeling can't be beat.
