I wasn't going to buy a screen protector for my phone for the exact reason that you stated - its made with gorilla glass - but just today I took my phone out of my pocket and there was a small but surprisingly noticeable scratch on the center of the screen.

I have no idea how it happened since I keep it in a pocket separate from everything else but needless to say I am pretty upset about it. I am really happy with my phone and haven't noticed most of the problems people are complaining about except my phone will randomly stop recognizing the SD card. This isn't a big deal but now I am considering returning the phone using that as an excuse so I can get a screen without any scratches (although I don't want to get a phone with the dreaded GPS issues people are talking about). Petty, I know, but I did just pay $350 for it.
So I just ordered a screen protector from Phantom Skinz a couple hours ago to keep this from happening again. Use the coupon code - summersale2010 - for 30% off your order.