Mine, I got it when it came out in 2010, used it every day since end of 2013 when I got the 5s. Screen is still in perfect condition, so is the back side.

That's mainly because of the magical super-slip coating on the glass back, isn't it? I swear my iPhone 4 used to slide off level surfaces.

Mine. Had it since launch. Not even a scratch on the screen either.

Which just goes to show, different people (ab)use their devices differently.