As I see it, QR codes have value in that they profoundly reduce the friction in getting someone to visit your service, business, whatever. If some one is strolling through the airport or reading the newspaper on the train or otherwise being exposed to your advertising, they are probably less likely to go through the effort of typing in a URL than they are to snap a QR. Make it easier on them, and they are more likely to come.
One the other hand, while the smart phones that are required to take advantage of QR codes are increasingly common, they are far from ubiquitous. I myself am a confirmed dumb-phone user because I think that data plans are a horrifying waste of money. Practically, that means that you are selecting a particular segment of your potential market. That might be a good thing if you are specifically looking to attract a younger and more affluent group, technophiles and early-adopters.
On the other hand, if you are looking to attract a broader, more general audience, I would carefully consider the role that the QR code has in my marketing. Don't rely on it too much.