The only reason I use a screen protector on my X is because of fingerprints. The bare naked screen shows fingerprints much more prominently than when I have a screen protector on. It also cuts down on glare.
At one point I was running my DX totally naked... no case and no screen protector... and I dropped my phone on the sidewalk and it SKID across the concrete FACE DOWN. When I picked up the phone... not a scratch! That gorilla glass is great stuff.