Does anyone have a sense of what percentage of the smartphone-owning population actually knows what QR codes are and would bother to scan them? I'm as technically savvy as your average HN reader I would think, and I ignored the things for years before finally spending the 2 minutes to learn what they are. It's always made me assume that the average person wouldn't bother with them.
I would imagine this might be a tad optimistic, mainly due to their use being limited to only a few forms of advertisement (print being the main one). The only time I can remember using a QR code was when I watched a stream of the Google I/O 2010 conference and they showed one to get a CR-48 chromebook. Needless to say, that QR code will forever be my favorite one.