updated 04:45 pm EDT, Thu March 28, 2013
New font, column sizes available
The update also introduces a wide column setting and additional font sizes, plus two new keyboard shortcuts: Spacebar now pages down, and hitting Command-W will close a window. Detail views have been tweaked to show "social proof" for favorites and retweets, and infinite scroll has been enabled for temporary columns.
TweetDeck is a free download and requires OS X 10.6 or later.