Wired recently ran a great article about Google Maps, but perhaps the most relevant content was in the side bar...

Discovering the New World
7 glimpses into the hyperlocal future.

The Internet of Things
What if you could walk down an unfamiliar street, use your camera phone to take a picture of a building, and instantly know everything about it, from the architect to the list of tenants. The technology to make common objects clickable, like hyperlinked words on a Web site, is available today in the form of 2-D barcodes. These digital tags look like empty crossword puzzles. Users create them online, print them out, and paste them around the city. Then anyone with a phonecam can "click" on them. A program on the phone decodes the pattern and redirects the curious pedestrian to a Web page. One project, called Smartpox, is using these barcodes to build online communities that center around, for example, scavenger hunts and restaurant reviews. Members slap a barcode on a given establishment, and in-the-know passersby can get the dirt on its crème anglaise. At Semapedia.com, you can drop in any Wikipedia URL to instantly generate a 2-D barcode pointing to the corresponding entry.

Read more here : http://www.wired.com/techbiz/it/magazine/15-07/ff_maps?currentPage=1