Latest stats: QR codes do work with 15% scan rate
Today's article in Adage gives us a few examples of successful applications of QR codes on magazine's ads. Key takeaway is that most successful ads (i.e. with highest code scan rate) don't explain how to scan them or what a reader will get after scanning.
Also, check this statistics from Lab42 on QR code already being scanned by 46% of social network users. Results are based on questioning unrepresentative sample of 500 users, but, nevertheless. But when you are targeting 18-34 group, you can be pretty sure of similar usage patters across the whole group.