I didn't put one on my 3GS and it has no scratches. But, I'm pretty careful with it to, never toss it into a bag full of random things (like keys) or anything. I got the Apple case for the iPad and no screen covering. By putting a screen cover on it, you're negating the advantage oleophobic coating, making it easier to wipe off. The only reason I might put a covering on is if I just couldn't stand the glare and wanted a matte finish (which will make the display slightly less sharp and less saturated). Do buy a case that covers the screen though.