[Martijn]

At Q42, the company I work for, we have a yearly hackathon. We start Friday morning and then depending on individual circumstances work until anywhere from Friday night to Sunday night.

We've covered last November's hackathon on tumblr: http://w00tcamp.tumblr.com/

One of the resulting projects is http://www.soundmatch.me/ -- enter your Last.fm username and it will generate a Spotify playlist based on your music recommendations.