Twitter will soon be adding something I've wanted them to add for ages - lists. In TweetDeck you can create groups, but most other Twitter clients don't support this. With the addition of this new feature I imagine most clients will begin to add support.
Lists are public by default (but can be made private) and the lists you've created are linked from your profile. Other Twitter users can then subscribe to your lists. This means lists have the potential to be an important new discovery mechanism for great tweets and accounts.
What they don't say is whether or not you'll be able to message a list - that would be useful, especially if you want to Tweet all your work colleagues for example in one go. I can't imagine they'll allow this though as it would also "encourage" Twitter spam.
