Personal record is something like 30 hours at a LAN-party. Played a mix of Warcraft 3, WoW and a little Unreal Tournament 2004. I don't really regret it, I man I had payed money to sit and game for three days, might as well get my money's worth!
I also played Mass Effect 2 for like 12 hours straight three days in a row when it was first released. I started playing the game on a Thursday and finished it the following Sunday. When I was done, I looked at my calendar an thought "I could have sworn there was a weekend around here somewhere."