I was passing by a museum last week, and they had some exhibit in the public space in front, and on the small board describing it, there was a QR code for a YouTube video of an actor narrating something related to the exhibit. The fact that the paternalist description of the QR code ("A kind of bar-code for the future [blah blah] go into the "APP store"[sic] and search for [blah blah]...") was more prominent than the code itself detracted somewhat from the feeling of being in the future, but that was the first useful application I've seen in the wild.
I saw a QR code that was printed a few feet tall the other day, letting you scan it from across the plaza; that's pretty cool. I still think you could build some pretty neat "worldly" easter eggs by hiding QR codes around cities.