I don't know a single person who has Facebook and doesn't check it on their phone. I also don't know a single person who doesn't hate how ridiculously slow the official Facebook app is. Fortunately, Facebook has APIs that allow third-party applications to do everything that you would normally use the official app to do - and it many cases, they do it better. A good example of "doing it better" is Friendcaster fro Facebook, which just so happened to receive an pretty massive update to version 5 today.
Even though FriendCaster Tab was "Honeycomb's first Facebook app," when it initially hit the Market it was, in a word, lackluster. It offered basic access to Facebook, but it was missing quite a few of the most commonly used features.
Since then, the dev has been hard at work completely redesigning the app - and the end result landed in the Market today. The updated app is similar to the phone version, but utilizes Fragments in Honeycomb, and it looks quite good.