My 5 month old sleeps so much better on his tummy; its a difference of 1 4-hour stretch then up every 1-2 hours on his back; or 2 almost 5 hour stretches on his tummy. (so only one wake-up overnight vs 3 or 4!)
I'm super nervous about letting him sleep this way (he rolls belly to back, but not back to belly)... curious as to how others feel.