Who in their right mind uses QR codes!?! As a human you have no idea where that thing is pointing, so why on earth would you trust it? At least with a URL I have half a chance of knowing if I'm about to be hit by a phishing attack.
You are at the mercy of the source of the QR code, with no real way of being able to validate it before scanning.
In any case, how are QR codes different from text URLs? Do you check the destination of every web link and/or button before clicking? Do you disable JS so that you can be sure that the URL displayed in the status bar isn't different from the one which will really be launched?
Like this: http://i.imgur.com/mlIr3QP.jpg