I think the ultimate application for this is actually advertising - eg, companies stick one of these permanently with a logo or something near a tourist trap, it detects when a flash goes off and basically imprints the logo into the original picture taker's photo.
There was an article on this yesterday on slashdot.org, basically the flash-detect logic is his own (so that it doesn't prematurely fire with red-eye-reduction pre-flash, for instance), but the basic concept is flashing a pre-developped slide backward through the camera onto whatever surface you want. Pretty slick invention, actually, but it's going to be annoying as all get out in real life.