Lists, a new feature we’re testing with a small subset of users. The idea is to allow people to curate lists of Twitter accounts. For example, you could create a list of the funniest Twitter accounts of all time, athletes, local businesses, friends, or any compilation that makes sense.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.
I use TweetDeck which has had groups for a while, but this is an interesting addition. Also … I wonder how many people will get added to a list named “spammer”