I’d like to send a very special shout-out to @SPLLibrarian. We chatted about QR Codes on Twitter a little while ago, and recently she shared with me an example about how her library is using them.
The Stratford Public Library has incorporated QR Codes into the outside of their building. Here is a picture of a QR Code on the book drop:

SPL Library QR Codes
After scanning the QR Code, people are directed to a mobile-optimized website that provides additional information about the library.
Congratulations to the SPL Library for moving full-speed ahead with making their printed materials interactive. We absolutely think that applications like this will help to increase the appeal of a library to today’s growing mobile audience.