I have never used a screen protector, putting my faith in the gorilla glass. No scratches or problems. I prefer the "feel" of a touch screen without a screen protector.
I keep my 1520 in the WindowsCentral store faux leather horizontal holster when it's in my pocket, so that helps to keep it protected from scratches.
Both my 640 XL & my wife's 640 have tempered glass and they have saved our screens from some catastrophic drops. I'll spend $25 on a screen protector versus $150 for a new screen.
