Could it work for libraries too? Imagine programs using QR for scavenger hunts... Using them to solve puzzles, find clues that send them off to read certain books... How about a "real life" choose-your-own-adventure tale? Let your patrons forward the notices to each other through phones... Play "guess the poet"... Link to public-domain novels online... Link to Project Vote Smart pages... Not to mention some of the previous ideas -- useful grafitti, this could be.
(Vid via Smoothplanet.)