Whenever I go to reuse a plastic carrier bag these days it usually disintegrates on me, so I don't think it's all that long before they start to break down. I do see the point about the damage caused by them though [those plastic things that hold cans together are a bit bug bear of mine; can't imagine the damage they can cause to wildlife and they don't break down]. I often park at Tescos when I go to the gym and then feel obliged to nip in and buy something, often meaning to buy just a couple of times but then get tempted to buy more. Also, buying something from, say HMV means that I have a cd in a plastic bag with a receipt so don't feel as if I'm walking out with something not paid for. I think, what I'm trying to say [I'm thinking this through as I'm typing] is the provision of plastic bags means people are more likely to impulse buy. Also, of course, people are using home delivery services more and more and the supermarkets would use plastic bags for that [I assume]. A supermarket I used years ago always had lots of cardboard boxes at the checkout that we used to put our shopping in, but I'd assume they get recycled now [and I suppose it looked quite messy, but me, being the clutter junkie that I am used to use them for storing things at home
].