@PartyBear: I think a lot of paper and lumber comes from tree farming these days rather than from virgin forests. Trees are cut down, but they are replanted so they can be harvested again in the future. I don't think that is much more environmentall harmful than the forest fires which take them down anyway. Plastic is more destructive to be made and never biodegrades, but that wasn't really what I was arguing.
@Ian Sane: I don't see why it couldn't be both a tiny plastic case, but still be inside a large cardboard box. Wouldn't this be the best of both world's? I actually have most of the cardboard boxes that my SNES, N64, GB, and GB games came in. Even have 1 or 2 NES cardboard boxes still, but most of those were thrown out because I just didn't save them back then.
My point is, if you take good care you can keep a cardboard box in great shape over a long period of time. I don't really have to keep opening or closing them because I keep the games inside the sleeves, cases, or third party storage solutions I have for them. I do keep the manuals in them, and that keeps them in good shape but I very seldom look at the manuals anyway.