Write a Facebook application

Something that I'm curious to try is writing a Facebook application. Now, I'm sure that many a developer has thought up some great idea, written an app, and then had it go nowhere, but I'm ok with that.

My idea is along the lines of a life list or things I'd like to do. I'm sure they already exist, and 43things is a website that does this very thing, but perhaps I could add my own spin to the idea.