Molly at DemoGirl has created a video that takes a look at several sites and their usability. On her Twitter piece, I could add a million items but one I would absolutely add is a way to do a multiple delete on the direct messages. Deleting one at a time is time consuming and my bet is that by adding a mass/select delete option, they could reduce by millions of messages.
Check out our 30+ usability tutorials.
Here is her video: