I sleep usually 6 hours on weekdays, and 4 through 10 on the weekends.
I like 6+ hours of sleep, because then I don't have as much trouble waking up in the morning, I am not tired throughout the day, and I can function good.
If I don't sleep enough, then I am tired and cranky.
I sleep as much as I sleep because it's generally the minimum amount I can sleep while still not burning myself out or being exhausted or tired all the time. Weekends vary a lot because sometimes I get paged after 2 or 3 hours of sleep (due to work), and I then wake up early, and work for an hour or two, and don't usually get to sleep until that night...