Re: Mithawk, and Dude's reply.
I don't recall reading some rule that the only way to solve difficult problems is to work on them for 80 hours a week. Sure, one can WORK for that long, but I'm not convinced about double-time as the best route to the SOLUTION. I suspect (as the studies Bostonian quoted imply) that the route to the solution is to be well-rested, relatively free of stress, and properly nourished as a general rule, with occasional bursts of extra hours (and concomitant increase in stress, tiredness, and/or poor nutrition) as needed. Creativity is typically a critical part of solving a difficult problem, and I believe that being tired and stressed interferes with creative (and general cognitive) ability.
When someone writes a paper that 40-50 hours a work is optimal, it ignores the fact that people vary in in physical and intellectual stamina the same way they vary in IQ. Ford was interested in hiring large numbers of people on an assembly plant. The law of large numbers meant that he needed to tune his work hours for the average worker.
But many times, intellectual problems can best be solved with small teams and don't scale well with many additional people. And for smaller teams you may well be able to find people who remain highly productive for considerably more than 40-50 hours a week. I could do ~60 hours a week in my younger days, but fell apart quickly with more than that. I knew people who could do more, and many people who were able to do less.
