The longest I have ever stayed up is playing EverQuest. I was finally able to grab a particularly popular monster camp to farm a rare item from a rare spawn (yes, one of those scenarios). It was during one of my high school summers, so fortunately I had infinite time to burn. I was determined to not let the camp go, and I ended up clocking in about 36 hours of playtime until I finally got my hands on the rare loot.
Needless to say, my head hit the pillow within a minute of looting that item. I do the occasional 8-10 hour binge but I will (most likely, depending on circumstances) never do another marathon like that again.