Ever since grad school, when I had evening classes and was first able to pull this schedule off, I would be lucky to be able to fall asleep before 3-4AM and I'd usually be up around noon.
I did this for years, and would usually shift it even later in the summer if I could because it gets so damn hot around here during the day, until another one of my ventures opened up a brick and mortar location and now I have to be in the office every day; luckily, I don't have to be here until 10~11AM, so I can at least sleep until 9AM, but it's been a rough transition.
In some ways I feel more productive on this new schedule - it's a lot easier to get in touch with traditional businesses and traditional business people, but it's killed my creativity - there are days when I do busy work until lunch and then screw around here on WF or gaming for an hour or two after lunch because I just can't get my mind working well enough to do anything creative until mid-afternoon.
A lot of you may have what one doctor thinks I have - delayed sleep phase syndrome. Basically, your body clock runs on its own schedule, not the schedule the majority of people have. You feel like your mind is racing and you can't go to sleep when you get in bed before 2-4AM because your body thinks that the late night hours are the middle of the day.