Had my iPhone 4 for 16 months with nothing more than a bumper. Never dropped it, never scratched it, nothing. I sold it in perfect condition when I got my iPhone 4S despite having no screen protector or hardcore case.
I decided that I was just going to go naked with my 4S and after 2 weeks with it it fell out of my pocket at a football game and landed screen down on the concrete. It had about 20 scratches on the screen and it was cracked in the bottom corner. I jinxed myself by telling everyone how well I take care of my phone. Fortunately Apple replaced it for me for free (despite their new policy about NOT doing that for the 4S) because I happened to know someone who works at the Genius Bar.
I have since gotten a Squaretrade warranty and started using bumpers again. I still refuse to use a screen protector or high impact case.
I decided that I was just going to go naked with my 4S and after 2 weeks with it it fell out of my pocket at a football game and landed screen down on the concrete. It had about 20 scratches on the screen and it was cracked in the bottom corner. I jinxed myself by telling everyone how well I take care of my phone. Fortunately Apple replaced it for me for free (despite their new policy about NOT doing that for the 4S) because I happened to know someone who works at the Genius Bar.
I have since gotten a Squaretrade warranty and started using bumpers again. I still refuse to use a screen protector or high impact case.