In complete contravention of what the bottled water people say is safe usage, I re-use my plastic water bottle many times before it usually ends up being thrown out, typically by someone else. Of course, bottlers of water have no vested interest in making sure that you buy more bottles instead of using the one you have, nosirree.
The latest study from the plastics industry (news article here) showing health problems with re-usable bags strikes me the same way. No bias from this source, either.
On the other hand, I am probably not going to be incredibly sympathetic to someone who got sick because because they brought vegetables home in a bag that they had previously used to transport used diapers. Those cloth bags are in fact washable as well as re-usable.