You will never guess, don't even try it. Here is the article that made Frans Bauma sad. Very very educational, highly recommended read (assuming that it is correctly written).
But what's even funnier is that none of those Sleep/Hibernate/Hybrid Sleep options work for my pretty decent new computer. It goes to sleep/hibernate/hybrid sleep but then immediately returns to normal functional state for no apparent reason (anybody knows how to pinpoint the source of the problem?). I guess they would have to duplicate the effort spent on sleep feature.