Great article on the New York Times about a study from Stanford showing that sleeping 10 hours a night improved the performance of athletes.
It's not just athletic performance that sleep improves--it's well-documented that sleep deprivation hurts work performance, emotional self-control, and even willpower.
The interesting thing about this study was how great everyone felt sleeping 10 hours a day. If you feel like you're not on top of your game, either at work, in relationships, or taking conscious control of your actions, consider resting rather than ramping up and working harder. A little laziness may refuel you!