At a simple level, it's obvious that they're at least somewhat successful: comScore reported 14 million U.S. mobile users scanned a QR code in July 2011. Usage significantly increased over the next three months, as an average 20.1 million users scanned a code per month.
The number of users who scanned a QR code, however, is just one measure -- and it doesn't reveal whether QR codes are actually successful. There are other metrics you should consider:
- What is the bounce rate from scans? In other words, what percentage of users who arrive at your website from a QR code leave without looking at anything else?
- What is the conversation rate from scans? If you want users to sign up or take some other action when they scan a QR code, what percentage of users actually do so?
Unfortunately, comScore doesn't provide statistics like that -- they're going to be unique to you and your strategic goals. Take the time to consider how users are interacting with your QR codes, and whether the codes are delivering what you consider to be success.