What's going to reduce your image quality more: the screen protector, or all the smudges your dirty little hands leave all over the screen?
I've already damaged the screen protector on my iPhone 4 by making the mistake of having my keys in the same pocket. Glad it was the protector that took the hit and not the phone.
I can't believe people worry about protecting glass.
Even when I had a very soft plastic screen Palm Pilot, a screen protector reduced the screen clarity more than 10 years of unprotected usage would, so I wouldn't use one even on a soft plastic screen.
On glass, total waste unless you have some other purpose than protection.