Rant aside, it is my experience that the vast majority of people are useless bums. Pretty sure that's nurture as opposed to nature, though. If it weren't learned behaviour, people wouldn't be performing all these rituals in the hopes of obscuring their very uselessness.
That said, I manage 4-6 productive hours a day. Used to be half that at the start of my dev career. Sometimes I do 10, even 12 hours if I have the energy and motivation.