Mike Hadlow:

I would submit that the appearance of hard work is often an indication of failure. Software development often isn’t done well in a pressurised, interrupt driven, environment. It’s often not a good idea to work long hours. Sometimes the best way of solving a difficult problem is to stop thinking about it, go for a walk, or even better, get a good night’s sleep and let your subconscious solve it[…]

To managers I would say, judge people by results, by working software, not by how hard they appear to be working.

Holds true for most creative work. It simply isn’t suited for a 9-5 work environment. 3-4 hours of hard inspired labor is often comparable to someone wasting away for days at time in other fields.