I admit the Facebook iPhone app is a little buggy, though I have to hand it to them, they have made a number of UI elements which now seem to be common place on the App Store.

e.g. IIRC they were one of the first apps to have a grid based menu system (ref: Google+ app, Bump, etc) and (I think) also the first app to have sliding menus (where the main view is slid to the right to reveal the menu hidden underneath the main view).