Earlier quoted context omitted.
QR codes on billboards and in marketing are kind of rubbish On a big billboard beside the freeway, sure. In a home for sale sign, or in a bus shelter, or anywhere else where people are either a) very interested or b) captive, they are fantastic.
The best place I've seen QR codes is on the tube. Because hey, I'mma scan this QR code, and then remember about it when I'm topside.
Keep your phone hidden (but check out this QR code!)