I was just watching a story about sleep deprivation on a science show called "Catalyst". One of the things they said in this story is that extensive studies into sleep deprivation has shown that around 15% of people can get by on (what would be for anybody else) insufficient sleep.
Apparently brain scans show that a different part of their brain kicks in when deprived of sleep and functionality tests (memory etc.) show minimal deterioration.
Interesting stuff, and could explain why some people naturally take to a polyphasic or light sleep schedule (I'm looking at you, Steve!) while others don't...