After some suggestions in the forum, I have dedided not to use a screen protector. Screen is scratch free so far (three months of heavy use); my only rule is keep the screen clean of dust (I use a special liquid for touchscreens), so as some suggest, maybe if you drag particles or dust can scratch the screen.

I had scratched my 770's screen when my dog, a 45 kg (100+ lb) Alaskan Malamute, decided to trample on it Just a single, almost unnoticable, scratch though.

My screen is scratched along the browser scrollbar line. It's a mild scratch and is not noticeable in most light. I assume it got there from a year's worth of using my stylus to scroll there. In retrospect, I would have gotten a screen protector.

I use a Martin Fields overlay, which is washable and re-usable and has done a fantastic job.

I use their overlays on everything I can -- N95 has one too.

Probably using a wrong stylus or pen by mistake usually does it.

I got mine a similar period and if you go in the sunlight and try different angles you can see some tiny ones (I suspect mahjong or how this game is called that my wife played on holidays - I need to blame someone else!) and few more where the scroll-down bar is.

All of them are tiny ones and I have the feeling that all caused when you tilt the stylus a little bit more and move. Dust should help too.