6-8 on average, with a bump to 9 or so on weekends. i have found that i can go for weeks on 5 hours a night, but i prefer not to. during school i would normally do 3 nights of 2 or 3 hours, 2 nights of 5 hours, and then make it up on saturday AM by sleeping for 12 hours straight.
my record is 28 straight hours of sleep, after doing a 50-hour marathon charette in architecture school back in the day. i actually had thought i only slept for 4 hours and it was not until halfway thru the day i realized it was Sunday, not Saturday.