Facebook's iPhone app is one of the most popular apps for the device. Version 3.1 brings some killer features to an already strong offering. Push notifications and address book sync, new in this version, are welcome additions.
Push notifications are a very logical addition. They have become Apple's compromise for not allowing apps to run in the background. Instead of having to fire up the Facebook app all the time to see if anything is new, you can now opt to get push notifications for new messages, wall posts, friend requests, friend confirmations, photo tags, events, and comments. This is way more efficient and allows you to only access the app when there is something new to check out, if you choose.
Facebook's new contact sync for the iPhone is particularly interesting. At first, I was a bit hesitant to try out the feature, worrying that it would overwrite the data that I had or add a lot of new friends on Facebook that I didn't really want as contacts on my phone. But it didn't cause any of the problems that I had imagined. Rather, it examines the contacts that you already have on your iPhone, trying to match it to a Facebook user. If it finds a match, it pulls down that person's profile picture, making it that his or her photo on your iPhone. It also adds other information, such as a link that takes you to that person's profile in Facebook's app. The feature doesn't seem to cause any data integrity issues, it just makes your iPhone contact information more robust. Even more interestingly, if one of your phone contacts is not your Facebook friend, it will (in most cases) still pull down their info from Facebook if it finds a match.
Version 3.0 was a big jump forward for Facebook's iPhone app. Even though its creator, Joe Hewitt, has since left the project and started boycotting iPhone app development, version 3.1 delivers some really cool features that round out Facebook's offering on the iPhone nicely.