We've been beta testing the new Adium 1.4 nightly builds for a couple of days, using the new Twitter functionality. Everything else is mostly the same (except Facebook seems more reliable) It works fairly well. If you want to follow along, go grab yourself the freshest nightly build.
Because the nature of Twitter is much different than other instant messaging services, you have to first let Twitter know it's cool for Adium to connect via a web interface. Twitter is also different in that you just get a stream of messages in one Adium window. Had they put each message in a new window, the app would become too annoying to deal with immediately. The one window updates every minute or so (see below
