My youngest daughter slept terribly for the first three weeks of life until she learned to roll over (yes, I'm serious) and then she slept fine...on her stomach. I watched her like a hawk, barely slept, but then I thought...why? For thousands of years, babies slept on their tummies. I personally believe that there are underlying factors with SIDS, and it isn't because they sleep on their tummies. The statistics don't really follow, either...when they say "twice as many die on their stomachs" what they mean is 2%, instead of 1%, which isn't nearly as scary as "TWICE AS MANY."
I was so paranoid with my first, she has a flat head in back. I would NEVER put her on her tummy, so then she hated it, in turn never spent any time on her tummy...sat late, crawled late, walked late. (Although she was talking to me before she could walk.) :)