When buying new rotors, does anybody get them turned? A buddy of mine is a mechanic and he always puts new rotors on a lathe and just skimms them. I've seen new rotors benefit from this.... maybe they were cheapies....

Typically you should not need to turn them. They are marked on the box to store flat to keep them from needing to be turned. By turning them he is removing some of the future life and truing them up. Meaning he doesn't trust them to be a flat surface.