The street-facing side of Tokyo's N Building is covered in QR codes that can be read by your phone for up-to-date information - including Twitter updates from the building's inhabitants as they happen.
The project is a collaboration between Qosmo and Teradadesign. Any mobile device that can read QR codes can access shop information, but more in-depth content like tweets (located by GPS tagging), coupons and reservations can be seen through a dedicated iPhone app that's available only by request.
Now this is a use of augmented reality I can really get behind: instead of cluttering up a building with billboards and sale signs, they're hidden behind an aesthetically pleasing QR Code design. More of this! Please? [Creative Applications via Design Boom]