Things They Should Research: plastic bags' route to the landfill

With all this talk of banning plastic grocery bags, I'd really like to see a user-centric study of how they end up in the landfill. A lot of the suggestions I've seen for grocery stores' alternatives to plastic bags seems to be based on the assumption that people bring their groceries home, unpack them, and then throw the plastic bags straight into the garbage. However, 100% of the anecdotal evidence I've collected (by asking everyone I've been talking to the last couple of days) indicates that people save their grocery bags and then use them to wrap their garbage or clean up after their pets. The bags do end up in the landfill, but as garbage bags, not as garbage. If we didn't have the plastic bags, we'd still need some kind of plastic bag to wrap our garbage and clean up our pet's waste, and that plastic bag would still need to go into the landfill. I'd really like to see some research or stats on user behaviour to see if these anti-plastic-bag people are way off, or if there's actually a "throw out the plastic bag" contingent out there somewhere.