all i can say is my wife had her i4 nude for about a week or so and she now has fine hairline scratches all over the front of the glass and a small nick. all she did was put it in her purse.
i feel like a broken record but:
co-worker dropped his i4 and it had a bumper on in the parking lot. chipped glass, pitted the glass.
friend dropped his i4 and it had a bumper on in the drive way. chipped glass and hairline scratches
cousin dropped his i4 and it had a bumper on in a death trap (gravel path) while biking. chipped glass.
mine has a full body IS since it came out of the box and wears a candyshell. I dropped it last night while getting out of my Raptor truck and it went down the driveway. thank god i had the protection!
i have another co-worker who could care less and its nude. he told me he dropped it 2 times already and go figure not a single nick on it
but he does have a few hairline scratches that he swore he "can't see".