If anyone else wondered I did a media buy with various QR banners. One of the best performers was this one:
http://i.imgur.com/SZ3eQ.jpg
I did 265,047 impressions on that one. My main objective was to see how many people would scan a QR code when they see one in the ad. Results: Out of around 600 clicks 13 came from people scanning it. Assuming that those clicks were generated as a result of triggered interest there are too few people willing to scan those online.
I also tried banners that only contained a QR code and nothing else with similar results. I tried crazy colours, animation etc. and each time saw similar results. I had 1/day freq cap too so you can assume that out of 265,047 people who saw the QR code only 13 scanned it. (Discounting margin for error, imperfect tracking, cookies, motive, artificial hits etc.)
-edit- No call to action. Maybe something like: "Use your phone to scan this bar code" would have worked better but I was testing the general savviness too. I suspect most people don't even know what that maze pattern square is.