As a motorcyclist, I think you should always stop to see what you can do. If you see a motorcycle down, try to shield his body with your car. He might be alive, but unconscious.
I really wish more people would take driving more seriously. If you hit and run, you're a piece of shit in my book. If I ever see it while riding, I will personally chase the piece of shit down and do some bad things.
Thailand and Brazil are the worst. You go down there and they'll leave you for dead.