TweetBot for Mac has been updated with just a .01 version, but the update still adds in some pretty powerful functionality. First of all, the update makes TweetBot compatible with Apple's Reading List service, so you can now add content to your Safari Reading List directly from the Twitter client.
There are a number of improvements added as well, and finally, TweetBot has added in something called "j/k navigation," where you can use your j and k keys to head up or down your tweet list. I am actually a big fan of this kind of navigation -- I use it to go through Google Reader all the time, so having it available on TweetBot will be a nice bonus. TweetBot for Mac is available on the Mac App Store right now for $19.99.