Stumpokapow
listen to the mad man
lol. I've never understood the "lines" thing. It's rarely happened to me, and a quick wipe with the smart cover and it's gone.
My smartcover is pretty discoloured and stained on both sides and leaves pretty visible smear/smudge marks on the screen when I open it. I use and carry my iPad a lot, but always either with my hands or snugly inside a laptop bag. I don't smoke and don't bring the iPad places where people do. I don't drop the iPad in dirt or anything. I have used the iPad and thus the smart cover after eating, but I'm generally a good owner. I have the sort of powder/baby blue colour smart cover with the grey inside.