TweetDeck User Streams preview brings real time Twitter to everyone
Twitter has apparently decided that the new Users Streams API is stable enough and the Twitter servers are ready to handle the traffic from a public TweetDeck release. The User Streams Preview of TweetDeck is really impressive, although there are still some kinks to iron out (I couldn't get settings to open, for some reason).
I suspect that allowing third-party clients to play guinea pigs for Twitter's newest and coolest API is preparation for real-time tweets in the official Twitter clients. If TweetDeck's very successful implementation of User Streams is any indication, realtime is going to become standard for any serious Twitter app.