The only thing that ever touches the screen of my Z is a screen protector. Nothing special, just cheap Belkin ones, they come in packs of 10 and aren't even made specifically for the Z. Sometimes I'll end up with the wrong size and have to cut them down to fit. When necessary, I can wipe them with a tissue, or a napkin, my t-shirt, whatever, because they're easily and cheaply replacable.
One of my coworkers has stuck with his 5500, using it for a couple of years without screen protectors. His screen has been very noticably scratched and scored by the stylus. You can see large rough areas of the screen where he's dragged scrollbars, pressed window widgets in the upper right corner, etc.
Makes me glad I've always used screen protectors.