Here is the first iPhone 4 drop test performed by iFixYouri - Nothing scientific, no editting, just holding the phone where you would normally hold it to use it, and drop it to the ground. They made sure the area where we dropped it had no debris.
Drop 1 - Ok
Drop 2 - Still Ok - Seemed to have turned off
Drop 3 - Landed on back - scuffs
Drop 4 - Cracked iPhone Screen
The 4th drop did it in.
Dont try this at home!