On QR Codes
Many insights in regards to mobile strategy overall can be gained at the flaws and failures/lack of current success of QR codes, namely from a UX perspective (poor software) and more importantly the context of the end user.
A QR Code Study
A study recently came out regarding the efficacy of QR Codes (or lack thereof) stating that nearly 80% of college students can't "figure out" QR codes.
Now, yes it is true (for the most part) what the study of 500 people (large enough sample size?) shows that many people either can't figure them out or get frustrated with the process. The latter is the part we and other mobile developers and designers must focus in on.
If the process of doing anything with your mobile device isn't nearly instantaneous then the user will give up. This is becoming hyper-sensitive in the mobile/casual computing space (is transferring to desktop computing and even waiting in line at Starbucks!). Performance and snappy responsiveness should be the number one user experience goal for any mobile application.
From my own experience with the various QR code readers on nearly every platform, Android is by far the fastest and most accurate when it comes to consuming QR codes. It actually makes consuming content/info from QR codes quite trivial. However, on Blackberry and even the iPhone the process is kludgey and utterly frustrating which I feel is largely the reason for the disappointment (and subsequent low numbers in the study). This is a software problem which can be solved.
Finally, where QR codes are super relevant are places where people have time to kill (think sitting on an airplane, back of a cab stuck in traffic, doctor's office reading a magazine, even sitting at home) and in places where people may be incentivized to scan them (think of getting a digital coupon on the label of a spaghetti sauce at a store). It appears the data supports this as well (58% are scanned at home, 50% scanned from a print magazine according to ComScore data). The context of the user should be a major consideration for QR code placement and ultimately the decision for nearly any/all things mobile.