Somewhere between 48 and 50 hours. I remember when I looked on the clock and I hit the 48 hours mark, but after that, I don't know how much more.
Still, it's not even my longest marathon of a game. I played LoL for almost 72 hours one time.
guess you don't require much sleep when all you do is sit down.
I think my longest WoW marathon was about 18hours long. I've done it only once though... not that much a fan of playing the same game for an extended period of time though, I'd rather spend a lot of time on the computer but cycling through various games.
My longest is around 14-15 hours, I wasnt really testing myself then I just had too much free time :D My limit is probably 18 hours... With drinking peeing and stuff of course