Althought its not a case, I have ghost armour (black carbon fiberon back and sides, clear in front) on my iphone 4. The Ghost armour was applied on front, back and all sides. The ghost armour protects the iphone from scratches, greatly reduce smudges on the front face and the carbon fiber along the sides greatly improve grip so the phone does not slip out of your hands easily.
I have several caes that I used on the iphone 4, but they were all bulky. When you removed the case, the back was always dusty with a possibility of that speck of dust scratching the phone.
Since I turned to the ghost armour, the phone feel great in my hands, it fits easely into my jean pocket or jacket pocket and finally it allows the phone to be showcased as it was designed, a work of art.