I mentioned my FF7 marathon earlier in the thread, but that was just the longest of many 24-plus-hour sessions I've had gaming. Of particular note was Labor Day Weekend 2005, when I played an entire Rome: Total War Imperial Campaign over a weekend, featuring a pair of 24-hour nonstop gaming sessions separated by about 10 hours of sleep. I've had quite a few "waking hour marathons" where if you don't count sleep I've played the same game to the exclusion of all else for over a hundred hours in a row...in the summer of '07 I took a week's vacation from work (10 straight days off from the close of business on a Friday through the whole next week and including a Monday holiday), went to Best Buy on Friday night, bought Knights of the Nine and Shivering Isles, rolled a new character, and played nothing but Oblivion, stopping only to eat, sleep, and crap (and my wife was great about it---she rolled a new WoW character and left me alone).
I did something similar with Morrowind last November---my wife was in Canada for 12 days visiting her family, I was unemployed, so role-playing ensued. For 12 straight days, stopping only to eat, sleep, and crap.