Saw this article on Ars Technica earlier, and had to try it out. Latest beta of Adium has a Facebook module. Sure enough, it works like a charm. I can see and chat to everyone just as if they had IM, all from the comfort of Adium.
UPDATE: It appears that by using this module, it continuously logs you out of your browser session. Trying to browse the Facebook site while logged into the IM client through Adium was a painful experience. Just FYI.