Well, if the screen surface on the N900 is anything like the N810's there shouldn't be a problem.

I've had screen protectors on the 770 and N800 since day one, and I believe they were needed on those. I actually also bought one for the N810 but was too lazy to install it before I started using it, and never got around to do it afterwards.

After almost two years of heavy stylus use, the screen surface is still, literally, good as new. I just always carry it in its pouch between uses, is all.

I sure hope the N900 is at least as good.