Tapbots has released an update for Tweetbot on the Mac adding a number of graphical tweaks and some new features, along with the usual bag of fixes.
Tweetbot 1.3 sports a new media timeline which allows you to hit Command + F and switch to the media view. A new look has been added to Tweet detail (including retweet and favorites), and you also get Profile Cover Image support.
To scroll the profile back to top, simply double-click the titlebar above a profile. To scroll the timeline/mentions/faves to the top, double-click again.
An issue with unread items obscuring notification/error messages has been fixed, along with a problem where text was still editable after sending a tweet.
Tweetbot for Twitter 1.3 requires OS X 10.7.4 (Lion).