I once stayed up 'til 1 in the morning once so I could be around for the Neopets score reset and hopefully get a trophy (which I didn't, by the way). But I got tired pretty quickly and was asleep within about a half hour.

Mostly when I stay up late it's because I'm talking to my boyfriend on Skype. He's kept me up 'til 3am before, but that's quite rare. I'm not a late-night person at all, I'm usually in bed by midnight, computer or no.

Edit: Though I'm often constantly on the computer from 7:30am until 12 midnight, occasionally breaking for school, food, bathroom, etc. So that's a long time I suppose XD