My brother was sitting on a tile floor reading his kindle and accidently dropped it - it hit the corner and basically it looked like the screen cracked. He emailed amazon's warranty service and told them that it fell from less than a foot and there was a well known weak spot in the corner. Amazon basically said, Okay, you're still in your 1 year warranty period and sent him a new one.

I've dropped mine while standing up and had it hit the sidewalk without it breaking.