When Tweetie tells me there's a new tweet through the menubar icon, clicking on it to reveal the timeline should remove the "new tweet" indicator. I realize this is probably a debatable decision but I find the current interaction quite annoying as it prevents me from simply opening up the timeline, seeing the updates, and going on my way. Since Twitter is all about looking at all the updates as a whole and then providing focus on specific tweets if desired, there's no reason to require someone to click the top tweet to remove the update notification.