All night and all day?? How the heck do you have any time to do anything productive!? For me, about an hour, maybe 2 at most. On Fridays when my buddy comes over maybe a bit longer like 4 hours.
Sometimes not at all.
On days that I do game, however, I spend 5-8 hours playing.
But most of my week is spent on my computer (10-14 hours a day, 7 days of the week).
Normally not that much. Maybe a half hour a day, sometimes not at all, and maybe 1-2 on weekends. MW2 has changed that considerably though. Now it's more like an hour or two a day and 3 or 4 on weekends. But that will decrease again.
About an hour or two like most of the fine folk here. Work and hanging out with friends brings that down a bit. Fortunately I have gamer friends so I get to play a little more than most.