I just found this site:
It is supposed to tag "physical objects" with the barcode of a wikipedia URL. Basically, you enter the URL of a wikipedia article, and it prints a chessboard-like box with black and white squares. You then glue this sheet of paper onto the object (after asking permission!), for example, a famous building.
The site also offers a Java software for cell phones with a camera. Anyone with that software can now take a picture of the sheet of paper with the cell phone, and the software will convert it back into a URL, which you can then open on the cell phone to see the article about that building.
I, for one, welcome our new tagging overlords! I am currently printing the URL of my user page to glue it to my forehead, so people can find out who I am without having to talk to me ;-)
Magnus