Research calls into question the requirement for 8 consecutive hours of sleep.
A fascinating article at the BBC's website (you can read it here: http://www.bbc.co.uk/news/magazine-16964783 ) details the research of historian A. Roger Ekirch into what may be a far more natural sleeping pattern of two 4 hour periods, with one or two hours awake between them.
One of the changes proposed for the current HOS was the elimination of split sleeper berth time. Maybe that's not such a good idea after all.
I'd really like to see some serious research done on this, since if it is indeed better than 8 hours in a row, it could have profound implications for reducing driver fatigue.