Basically it was awesome. I met a bunch of great people, sang along to The Final Countdown several times, and just generally had a blast being in such a productive climate. I helped brainstorm some ideas and offered feedback here or there, worked out some basic for a trick-taking card game with my good friend Tom Sarsons, and composed the music for two games: Pump up the Jam and Bullet Cell (links over there ---->).
I guess what I'm saying is, if you're interested in any aspect of videogame production, this is absolutely an experience I'd recommend.
Last year GGJ won the Guinness World Record for largest "game jam," and from what I heard it was even bigger this year, but I'm not sure whether 2013 set a new record, so I may or may not have helped set a Guinness World Record, but I will still aid in the production of any novelty oversize foodstuffs just to be safe.