I have little tiny "dents" in some spots of the back of my phone which seem to correspond with little marks on the agent 18 case. Im guessing dust or something got caught in there and caused it.
My Agent 18 Eco case hurt my iPhone 2G as well. I could see black scratch lines on the back of the phone that lined up with the molding on the inside of the case. Needless to say, I won't be using Agent 18 cases again.
incase protective cover works just fine. The new model for the 3g seems better than the old. It seems more "rubbery" and less prone to stretch and cause scratches.