This needs to be said, butt in chair hours =/= work hours. My brain is constantly thinking about problems I'm trying to solve or what I need to do next. At home, at work I often will be thinking of things and walk to my computer to either do them or note stuff down. My best hours aren't all at the office since often there is a lot of other things that interrupt me there.

Peopleware should be required reading in startupland.