I also put a skin over the front ("Best Skins" is the brand, I think), it's made of indestructible stuff, designed to protect helicopter rotor blades. I can believe it -- this stuff is unbelievably tough. It's also nice and clear, and, adheres nicely to the glass (you need to spray the adhesive side of the skin with a soapy water mix (they have directions) before applying it, so that you can position it when putting it on the glass -- takes about a day or so to cure after that, during which time it doesn't look nice -- but when it cures, the water is gone, and it's crystal clear). I use that stuff on all my players, its great. I originally bought pre-cut skins, but now I buy "bulk" sheets from them and cut to size with a sharp scissors (you will NOT cut it with anything else, including a knife -- it's amazing material). I cut pieces to cover the display-only, instead of the entire player.
The glass on the Zune 80 IS very strong, but, it CAN scratch -- the first one I had, which died and was replaced by MS, came out of my shirt pocket with a scratch. I had been very careful with it, always keeping it in a pouch (this, before I got the case), but one of the FEW times I put the player in my shirt pocket without the pouch, it got a scratch in the glass. There was nothing sharp in my pocket, so I assume it was a piece of dust or sand that may have blown into my pocket (some dust can be incredibly hard and abrasive).
When they shipped me the new one (I was expecting them to return the old one, repaired, with the scratched glass) the first thing I did was put the skin on it.