Some interesting uses for Twitter
Enter a few words or phrases to see how often they have appeared on Twitter - since March 2004.
Good for seeing twitters from a group of people. I prefer Twhirl because it can be transparent on the page and it's a bit simpler.
If I was doing more tweeting/ following more people who I wanted to group - or I wanted some of the extra features in TweetDeck then I would re-install it to use instead of Twirl.
List of other Tweeters with an interest in Usability
Several features including telling you who stops following you.
Several features including: Tells you the last twitter you made before someone unfollowed you.