QR Codes can be a useful item, but like any of our other tools it should be used well or its better to avoid them.
It’s like putting a url on an ad or promotion, you need to think through what the QR code will give them for their time and effort to scan one. Everyone wants a payoff for doing an action, so if you are asking them to scan a QR Code you should think about what is that payoff for the user, a discount, exclusive content, of a sweepstakes entry? Keep in mind that they are probably coming from a mobile device as well. A standard webpage may not be the best experience for the user on a mobile device.
As anything we use, the technology should be a benefit not an annoyance.