Here's a quick, inspired talk about brain-dead uses of QR codes. The takeaway: Every time you use a QR code for something and don't think it through, a kitten dies.
(Or see it here on YouTube.)
One other ill-considered use of QR codes he didn't mention: When marketing to older people -- i.e. fundraising.
Show your compassion for the world's kittens: Lay off the QR codes. Until you have donors who actually use them.