John brought this to my attention a while back, and I thought I'd pass it along. First things first, what's a QR code? Basically, it's a barcode that you can create, and that mobile devices can scan. They're a bit smaller than your traditional barcode, which makes them easy to slip into printed marketing materials. This linking from physical world objects called a hardlink.
Great, but what can I do with it? Well, here's an example. You're putting on an art show, so you post a flyer downtown. Someone is interested in the show, takes out their mobile phone, and scans the QR code that you've put on the flyer. They can instantly get more information about the event, and a link to a website where they can check out the artists or buy tickets to the event.
You can effectively make all of your printed materials - business cards, posters, etc. - more interactive. Scanning the code can lead the user to additional text, a web link, or other data. Anyone with a camera phone equipped with the right reader application can scan QR codes. Google's Android supports their use, as does Nokia's Symbian.
These codes can be used to link printed marketing campaigns to their online campaigns, but I think there is a lot of room to be innovative with the kind of information you're giving people. These are apparently already pretty big in Japan, but are finding their way into media here as well. If you'd like to find out more, go to www.qurify.com.