Flyar is a quite interesting Mash up between AR & Twitter. It's a free Twitter visualization application that uses Augmented Reality and gesture interaction. You can set it as your screensaver or just play around with it.
It uses your webcam to create an augmented video image, enabling you to visualize incoming tweets (from your account or a general feed) in a twitteresque setting that you can interact with.
Check it out: http://ww2.ydreams.com/flyar/