If you've visited the site in the last couple hours or if you helped test it yesterday, you are now seeing a redesign of the site. The previous interface was a hack, too spacious, and even we were getting tired of that green. Tweet Scan now takes up less space on the screen and uses strict(er) css for a standard layout no matter which browser you prefer.
Additionally, we wanted to put a new thingy(that's an accepted word now right?) on the page. Google has their Zeitgeist which is cool but having something that updates once a month or even once a week is glacial by Twitter standards. Our Popular Searches div updates once an hour and reflects some of the most popular searches of the last 24 hours.