The "factory provided" screen cover actually isn't a screen cover at all, just a cheesy piece of "shrink wrap" like you peel off of many things these days. Get a real screen protector, like the Boxwave Clear Touch. As for your styli, any dirt or grit on the end will do a number. Take a good look under a hand lens - if there are any small imperfections causing the problem it should be possible to buff them down.