I think they have so many applications that they can't just be a fad. What will be fads is how they are used. It's like someone saying that barcodes are 'a passing phase'. I have played with them a few times. Usually using Google's API Google Chart Tools / Image Charts (aka Chart API) - Google Code and some forms/php to feed the info in.
I worked with some guys who own a company called QRky - QRky | Welcome to the next generation business cards | - they specialise in branding people / products with QR codes, they're pretty into it so may be worth checking their blogs, twitter (@qrky) for up to date knowledge :icon_smile:
It applies to anything. You scan the QR image and it sends the information to your phone automatically. You can attach anything to it ie. location map, web address, contact information, any type of content, etc. I think the only downside is (and correct me if I'm wrong) is that its only smart phones that can access the information.
The idea is good though as it can be applied to marketing and saves time for the user by just being able to scan the code without having to input any data themselves.