Update: URL shortening appears to happen in the background, without you choosing which shortener to use, and the shortened URL length is reflected in the character count.
Original post:
It’s been waaay too long coming, but Twitter finally released version 2.0 of the Mac Twitter client formerly known as Tweetie. Finally we can see native twitter retweets (an implementation I still don’t like, but it’s a fact of life in Twitter now, so clients need to be on board with it) and a slicker, more modern interface.