The new issue of Popular Sciencehas the world's "first interactive 3-D "augmented reality" magazine cover."
How does it work? Just head over to popsci.com/imagination, launch the viewer window, and hold the cover of the magazine up to your computer's webcam — you'll see a 3-D landscape dotted with wind turbines pop off the page; by blowing into your computer's microphone, you can even make the turbines spin faster.
This sort of thing has appeared on Slog before (I can't locate the specific post), but I believe this is the first mass-market application of the technology. I still can't see exactly what it's good for except being cool.