Yes, I would imagine over time it would become slick like the touchpad does on laptops. But at least you get two in the package.
Oh, and speaking of oily spots...I asked one of the guys at the apple store what was best/ safest way to keep the touchpad and keyboard clean on the laptop, since they are are in constant contact with hands and skin oil, etc. I have an old powerbook and the touchpad is almost useless now. Anyway, he suggested mr clean sponges. I bought a package, and so far they work wonderfully (and make white macbook look great for months now). So maybe that's an idea to keep a covered iphone screen clean? They seem to remove build up quite well, and one sponge can be used several times. Sorry for the o/t.