[sic1]

They are using jQuery. Their code is obfuscated, so hard to say exactly how they are doing it. But i know how I would do it. Nothing crazy going on there.

You fetch your tweets from twitter, and build your html for them, position it out of view contained by an overflow hidden div. Go through the list of tweets, waiting a random amount of time to send them all off, and animate them from the bottom to top over another random amount of time. Im sure the biggest details will be in tweaking the timers so you get them firing off well. On animation callback, run the script again on the element.