The longest single game session I've had would probably be when I played FFIX for 19 hours straight, and I didn't get anywhere either... It was all sidequests. I know I must've played FFXI for longer than that in one session but I forget how long that would be. There's other games like Suikoden V and stuff that I've played for the entire day, but I didn't note the time like I did with FFIX.