I went to Berlin over the winter break with various and sundry Noisebridgers to experience my first Chaos Communication Congress. While there I discovered c-base, a combination hacker club, nightclub, and crashed alien spaceship. Closest thing I've seen to the set of a Doctor Who episode, ever.
c-base has a multitouch table they built (with a projector inside, mirror, infra-red illumination, and a diffusing surface), and they had a little hackfest to write things for it. With lots of help and inspiration from two graphics hackers I met there, Martin and Ulli, I wrote multitetris.
Dan Kaminsky calls it the "Minority Report of Tetris". Good times. Man, I miss programming for fun.