Gwibber is an open source microblogging client for GNOME that supports Twitter, Jaiku, Facebook, Pownce, Identi.ca and other popular social web services.
Yes I know its not Tweetdeck but hey hello, it supports more account types than just Twitter and Facebook. Its also got interesting support non microblogging services for Flickr, Brightkite, Digg and a few others. I've been pretty vocal about knocking Gwibber's stability in the past but now its rock solid. Currently I have 7 different accounts running through it and it doesn't even blink. So solid, that I have dumped the Air app Twhirl. The only thing which I have seen which is close to Gwibber is Eventbox/Socialite which is mac only. There's already talk about making a QT version of Gwibber which could work on the Windows and Mac platform too. I expect most people will look at it and say, yuk. But to be fair its using my own custom style from ubuntu, and it will get better. The concept of Gwibber and how it works puts it a few steps in front of a crowded microblogging market.