Layer (s) of Reality
Layar is an application for your phone (with an additional iPhone application coming soon) which layers over what you can see with the phone camera. Basically, you can add a layer of anything over top what the phone says assuming it is spatially referenced. Imagine walking down the street, pointing your camera down the street and seeing all the real estate for sale there, or all the Yelp reviews, or even historically referenced information (such and such lived in that house). The creator was mentioning the real estate, Twitter feeds and job opportunities as the first examples, which makes sense.
Think of the opportunities for teachers as the Ignatia Webs blog mentions as well. Taking education out of the classroom and into the physical realm. Language students walking down the streets, pointing their camera at something and identifying the vocabulary word or phrase of what it is. The historical examples mentioned below. Novels like Ulysses (or Dubliners) or Catcher in the Rye (or any Salinger) spatially layered over Dublin or New York City. Take your own literary tour, with additional layers for historical information, quotes from the text and critical significance.
Plenty of opportunities!