The "Why we sleep" book is just full of facts about the difference between a good nights sleep and a lack of sleep. There are so many things that fall apart when a few hours are taken off and nobody can be conscious of it, even though they are very very measurable. He also discusses thing like how two groups of people get a night of good sleep, they learn something and get 3 days of quality sleep. Then one of the groups has their sleep limited by several (3/4?) hours. The following day they get full nights rest, and the next day they are tested on what they learned earlier in the week and there were significant deficits for the group that had that one night of bad sleep in the middle of the week.
After reading about it, I've learned a lot more about sleep, but the greatest effect is that I really appreciate sleep more, make lots of time to optimize length and quality. Knowing all the info in the book it would be difficult to justify using an alarm clock to force yourself to rise before your body is ready.
Really cool book.