Researchers at the University of Pennsylvania have discovered the people who don't sleep well tend to eat more than people who do, and that they do not burn any additional calories.  This doesn't mean that insomnia causes weight gain, but does show that sleep is important. 

More research will show more about how the two impact one another, but I can tell you that I find my body craves certain foods when I'm tired. As a matter of fact, right now I could eat some fried shrimp...