I actually believe that the optimal amount of hours depends on the work being performed.
For coding and hard sustained mental work, I believe 8 hours is way too much. That doesn't mean they don't have to think about the work after leaving work - there was an article recently on HN about thinkers having breakthroughs when going on long walks. Maybe a flexible schedule would work best (short burst of intense 80+ hours of coding are also common but not sustainable).
OTOH there are many other kinds of work where working 60+ hours is sustainable long term (though I would advise against much more than that, there's a life to enjoy too!).
For coding and hard sustained mental work, I believe 8 hours is way too much. That doesn't mean they don't have to think about the work after leaving work - there was an article recently on HN about thinkers having breakthroughs when going on long walks. Maybe a flexible schedule would work best (short burst of intense 80+ hours of coding are also common but not sustainable).
OTOH there are many other kinds of work where working 60+ hours is sustainable long term (though I would advise against much more than that, there's a life to enjoy too!).