I sleep 8-10 hours per night, on average. I have bouts of insomnia, but my productivity drops significantly if I sleep less than 8 hours. I also start to have very odd - and dangerous - physical symptoms. Yes, I have a sleep disorder. For a period of time right before I was diagnosed, I actually slept 14-20 hours per day.

As with most constraints, it has turned out to be an advantage in some ways. I focus on working smarter instead of harder, and I really value the hours I have to work with in each day. I have some employees that can accomplish more in one hour than other employees can accomplish in a month. A few hours each day can just be a rounding error if you are really conscious of productivity and smart about how you use your time.

The idea that you can only sleep 3-4 hours per night if you want your startup to be successful is complete BS, and is part of the counterproductive macho aspect of startup culture. If you can get by on 4 hours of sleep, and aren't lying to yourself about your productivity and performance, then good for you...but such people are rare.

I wish I didn't have a sleep disorder, of course, but I would still sleep 7-8 hours per night even if I didn't. Brains function best when they are well-rested.