I had the one from the box on mine for a few months until my stylus developed a sharp edge (no idea how), and one evening I noticed a few annoying scratches on the protector. I got a martin fields one from ebay and when it arrived I was a bit worried about taking the old one off (ie would it damage the screen).
Luckily, it's easy. Just get your nail under a corner and peel it off, it's nowhere near as sticky as it seems.
Applying the martin fields one was just as easy (maybe I'm just a natural
). I think it's much better than the one that came in the box - it feels a lot smoother and the screen does seem brighter (might be the placebo effect).
I've had it on for a month and wouldn't hesitate to get another martin fields if mine got scratched. I didn't bother with the camera hole protector (I can't see the camera hole being that likely to get scratched), and I also didnt put the one for the bottom buttons on (it doesn't fit perfectly and the touch wheel is half covered making things like zooming in opera a bit more tricky).
As for cleaning the screen, I just wiped it on my shirt (cotton) which got it perfectly clean pretty quickly.