Do you really need case?

[xiang2011]

It's wondering... as it seems some people instantly put on a screen protector and it never leaves the safety of a case, so how do they know if it's really needed?

I've used my iPad naked since launch, and despite some minor rear scuffing, the rest is mint. So if one is moderately careful, will an iPhone get damaged from normal usage? Just how easy is it to scratch the glass? Does anybody use their iPhones naked, or in/out of a slip iPad Case?