The Facebook app for iPhone sports a shiny new upgrade today, and even if you pretend to enjoy Facebook purely ironically—like me—you'll probably like the new features.
First up is push notifications. You can choose which events send you notifications and, perhaps more importantly, which don't. I like instant notification of new messages, wall posts, and comments, but I'm less interested in knowing the second I receive new friend requests, event invitations, or photo tags.
Perhaps even cooler than push notifications, though, is the new iPhone contacts syncing. The Facebook app can automatically pull down your friends' profile photos and update your contacts accordingly. (You also get to choose whether existing photos are overwritten with images from Facebook.)
The Facebook app is free, and requires iPhone OS 3.0 or later. At this writing, the new version isn't available for everyone in iTunes, but if you don't see it yet, you should soon.