An interesting research:
Sleep less, live longer?
You only need as much sleep as you feel you do. If you can do fine with 5 or 6 hours a night there's no need to get more.
Someone above said that successful people tend to sleep less. I think it's true, but only because they're so excited about life and goal-driven that they can function normally even with some less sleep. They're so excited about life/goal driven that they barely feel the effects of sleep deprivation.
Most people who think that they need 8 hours of sleep a night actually don't need more than 6 and a half hours. I was like that, used to need 8 hours of sleep a night but i've been very busy lately (in a good, exciting way, not in a "i work like a slave" way) and it's done wonders for my sleep; i get really great quality 6:30h of sleep a night and feel no need for any more.