Got my iPhone 4 the day they came out and never had a bumper/case on it. Dropped it many times - onto wood, tile, furniture... never a scratch.
...Until about a month ago when I dropped from waist-high and it landed directly on its corner.
On concrete. Shattered the front glass and cracked the back glass all the way through in two places. Yes, I cried.
Looked at my options and was dreading taking the phone apart to replace the parts - and I hated the idea of a $200 Apple replacement even more.
Went to the Apple Store with no expectations, no attitude, and no excuses. They gave me a new (maybe refurbished, but perfect) phone. No questions asked, and no charge.
Two results of this learning experience:
1. The next computer I buy will be another Mac.
2. I have the Apple bumper on the phone now.