My boss has a couple of children, and he is very much a night person. He'll be working on stuff till 2, and then be up again at 7 because of the kids. I'm sure that isn't healthy either, but that is when he is most productive.

I myself have found myself to be more productive at night as well. For some reason I am just able to get more work done, faster, and more efficiently and best of all with less distractions from "the real world".