I never use any screen protectors as I always found they either didn't fit right (leaving unprotected gaps that collect dirt), look like crap (as especially due to the previous issue) and how on earth do you get the thing dust/smudge free enough to apply it without leaving marks underneath?

I find its easier to just forget about it as the default coatings are usually pretty decent, as long as you do not accidentally put your keys in the same pocket.

I have a soft cover I used on my Xperia X1 that I suspect might just fit over the N900, I will use that. That is enough to stop things rubbing on the screen in my pocket, actually in-use the screen should come into contact with anything sharp enough to damage it - unless you drop it.