I don't have my iPhone in a case. If you can't see how beautiful and thin it is and stuff it in a case whats the point of having it? The screen and back won't scratch unless you drop it on concrete.
Personally I have never bought a phone because of how beautiful and thin it is. I'm not one to show off my phone but to each his own. If the one I have wasn't made out of Kevlar and gorilla glass I would probably have a case on it. To me the point of having it is to make life easier for me and for emergency's if I break down.