A QR code is 2D bar code that was standardized well enough that free decoders are readily available for computers and smart phones. You can encode about 3 KB of data according to Wikipedia, and this data can simply be text. The most common use seems to be to encode web site addresses that will be loaded in a browser automatically after the QR code is decoded. Because it's so easy to generate your own codes, just about anyone can set up their own scavenger hunt by hiding a bunch of custom codes locally and simply requiring players to write down what the codes say.
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By adding just a little more structure to this concept, you could orchestrate stories that enforce finding QR codes in a particular order. The Hyperlab at Carleton has done a lot of research on writing narratives appropriate for this kind of scenario. A GPS-based system called Whereigo facilitates the creation of stories and games that are tied to location. Combining these two ideas would allow for finer grained placement of interesting story pieces than is possible with GPS alone.
I'm currently working on an iPhone app prototype for QR-based stories. If it goes well, I am thinking about creating an authoring tool to make it easy for everyday users to create their stories, then polishing and marketing the app.