I'd say 10 hours a day is an average...
my work requires that I be in front of a computer, though (I'm a programmer, heh).
I rarely can bare more than 12 hours a day, else I get sick and disgruntled... unless it's about playing in a LAN party, then we can do up to 15/16 hours - great maximum. I don't believe the guy who tells me he can do more
