Those of you that are on Tweetdeck will notice that you can make more use out of the service by requesting to use more API calls. API calls include sending out tweets, following, and unfollowing people. Users can also request more tweets at a given time. The original API limit was 100 per hour and now it is 150 per hour.
Other applications that have seen the API limit being increased includes Twhirl, Tweetie, Tweepular.com, DestroyTwitter, etc. What this probably means is that Twitter is scaling up their server architecture to handle tons of additional bandwidth.