This is totally user preference. Fine scratches can happen but doesn't mean they will, so if you think you can be careful enough not to have sharp objects near your screen you'll probably be ok without one. As for myself, I prefer the added security that comes with having a screen protector on all of my iDevices. I use a Power Support HD screen protector on my 4 and soon to be 4S. Power Support protectors are very easy to apply and usually go on nicely on the first application.
Are the power supports good then? I'm trying to hunt one down that's easy to apply, after the Best Skin Ever attempt, I'm not impressed.
In my opinion, they're great. I've used them on all 3 of my iPhones, and the iPad 1 and 2. Supper easy to apply and believe it or not it went on correctly the first time I tried even on a screen as big as the iPad. You can get 2 protectors in a pack now for $14 which I think is a good price considering the protection that it offers.
Yes they do get small scratches over time. My last one I was SUPER careful with it and thought I was scratch free. I looked one day at the screen and when turning it slightly and getting the right angle, sure enough there was a scratch.
My husband removed every protector I put on his and within 24 hours of removing the last one he rendered his screen damn near useless. He had it in the same pocket with his keys and sat there all day with a key gouging at it, and it's not eligible for replacement bec it's "cosmetic".
I scratched mine up pretty bad. I had an extra one laying around. I messed up putting that one on. Right now, I can't seem to get this one air bubble out where i bent it taking it off. But i read up a little bit on how to clean them and minimize air bubbles. Cleaned it like 9 times. Surprised the adhesive is still there. Used tape to remove dust. Have like 3 tiny bubble specks, but no biggy. I needed that thing.
no WAY am i going to go without a screen protector or case
I strongly recommend a screen protector, mainly because you never know when you may accidentally scrape something, be it your keys, when you slide your phone into your pocket. I really like the Zagg wet application screen protector. I found it easy to install and has a life time warranty on it. They are a little more money than the average screen protector but in my opinion are well worth it.
My husband has a cheap matte finish screen cover from ebay and he really likes the feel of it and has held up just as well as my Zagg.
I use a Zagg screen protector. It gives you the protection and it still allows you to have the benefit of the retina display. I've used other protectors from AT&T, those would always have air bubbles, took away from the beauty of the screen and weren't compatible with my case (screen protector would always lift when I took the case off and on).