With newly-announced support for Facebook, you're going to need some more real estate. The release comes two short days after Twhirl frontman Loic Le Meur announced that Seesmic had released a standalone Facebook app which, like TweetDeck, is built on Adobe Air.
Setup involves logging in to Facebook and the usual two or three clicks afterwards. Once completed, you'll have a new panel showing your Facebook friends' updates and a checkbox next to the update field to enable posting to Facebook. Curiously, TweetDeck includes the ability to email or tweet Facebook updates, something which doesn't necessarily jive with Facebook's TOS.
For now, that's about it for functionality. You can't, for example, send replies. With TweetDeck's history of Twitter kung-fu there will likely be plenty of enhancements in the coming months.