So far I've been mostly lucky. I haven't broken my screen, but I did at some point develop a crack right off the headphone jack that wraps around to the back. The battery lid doesn't snap properly at that corner, but other that all is good. Fingers crossed.
When I had my iPhone4 I had it on my lap while I was driving to work and forgot it was there. Jumped out of the car and started walking before I realized it had hit the ground (face-down) and I stepped on it smashing the screen. Luckily Apple has a policy where they give you a new (refurbished) device one time, so that's what I did.