I think the longest I've spent gaming is in the 8-12 hours range and not recently either. When I first got my PS3 I was up until the early hours playing Fallout 3, the quiet of the house and the barron landscape just seemed to fit. I also did a mega session of Valkyria Chronicles on my first playthrough because I was really into the story, that was probably my last late night gaming session that wasn't a drunken attempt at Fifa or Street Fighter 4.
To be fair, I've never seen the point of staying up for so long playing a game, I like my sleep, the game will be there in the morning. Though I wlll be honest, I'd give anything not to be working tomorrow so I could finish Dishonored, I can't be that far off the end.