Facebook has had a XMPP gateway (same protocol as Google Talk) for a while, but you need to have a username (e.g. www.facebook.com/zuck instead of a long number) to use it. I kind of liked resting in the very small measure of anonymity that not having one provided. However, a while back Facebook assigned usernames to everybody who hadn’t already picked one.
It just occurred to me today that means I could plug Facebook into Adium and keep an eye on who’s online without to keep a tab open in Chrome. If you want to do the same, just follow the instructions provided.