Although hardly empirical, this small study does give some indication about the effectiveness of those mostly aggravating little QR monstrocities popping up everywhere.

From Lab 42's post: "This survey was conducted online via social networks from July 28 to August 1, 2011 among 500 social media users. This online survey is not based on a probability sample and therefore no estimate of theoretical sampling error can be calculated."

Frankly, I'm looking forward to the day when recognition software allows you to take a picture of anything, including an ad, linking you to further information.