I'd stay up watching my boyfriend play Fallout 3 and Mass Effect until 3am since they're pretty awesome games. I especially loved Mass Effect. <3 As for myself, maybe not lose sleep over but any Rock Band or Guitar Hero. Once I get started, I keep going for hours, even when the pain in my fingers overtake my body, I keep playing til I beat all the songs on Expert.
Or til I get pissed off and throw my guitar down and put ice packs on my fingers. Oh, and a silly MMORPG, MapleStory. Generally from grind sessions and too much chatting. I use to stay up til 2am training and had to go to wake up for school/class at 5am. Or I had an 8:15am class in college. But I quit that game a good year ago. Nexon can go shove it. Sleep is lovely.