I've always used an anti-glare screen protector. I'm not so worried about scratches, but the glare is a massive issue for me. I'm not really keen on seeing my face staring back at me when I'm trying to read or watch a film.
Because of the retina display, I thought I'd try not putting the PS anti-glare on at first. Half an hour in my office this morning and the overhead lights were driving me batsh*t crazy, so the PS anti-glare has gone on and now I can actually use the iPad.
If I didn't work in an office that has overhead lights then maybe I wouldn't be so bothered, but your environment can dictate what's best for it.