Inspired by some recent internal work in inventorying items using QR codes, we thought it'd be fun to make a system that lets Sunlighters print out QR codes for anything they wanted.
Cool - some recent experience with QR codes and my blackberry has taught me that they don't always work as well as you'd like, although it might depend on how good your camera is.
What I've always wanted to see is a system that associates QR codes with a mobile friendly web forum. You could then tag a physical object in the real world, and when someone clicks on it they get a discussion that they can contribute to, and they can see what other people who clicked on the object wrote.
Sort of a way to build an online community associated with a physical location that you actually have to travel to that location in order to access.
You could take this a step further an actually integrate it with a social networking application like facebook, so you could indicate that "I wuz here" and meet other people who hang out there too.
Of course, given that phones now have location capabilities, you could use GPS for this instead of QR - but I'm not sure that GPS gives you the level of granularity required to differentiate, say, different bars in closely packed neighborhoods like the lower east side.