The bottom line according to the Wall Street Journal: that reusable tote bag, whether it's free or $25 or $300 on eBay is only green if you use it—a lot.
The issue is that some reusable bags, such as those made out of polypropylene plastic, take 28 times as much energy to make as a disposable plastic bag and eight times as much energy as a paper bag. So, to break even from just an energy point of view, they need to be used on a regular basis, not just every now and then. We have at least three reusable bags sitting around the house unused, so that means the next time we're tempted by one that's especially attractive—or free—we'll have to just say no.
Article and illustration via WSJ.com