iDevices are among the best-built products in the world because Apple has very strict rules when it comes to the quality of its products. Apple promotes iDevices as having scratch-resistant screens, and the newer Retina Display screen as being much stronger than the screens used in previous models. The iPhone 4 and its Retina Display were tested and unfortunately they failed the test, cracking even worse than that of an iPhone 3GS, although the iPhone 4 terminal had a bumper case installed. From my experience, the iPhone 3G scratches quite easily both on the back and on the front, but the iPhone 3GS is no exception, at least on the back, I didn't manage to scratch the front.
I use an InvisibleSHIELD kit to protect the phone because I'm a bit clumsy by nature and if I didn't have the film on the screen then I would definitely be looking at some pretty deep scratches. Apart from the iShield kit, I don't use any other case/cover because in general, once installed, they change the shape of the phone and I prefer to keep it as "lightly" as possible.
What cases/films do you use for your phones? If possible, give a link.
