From the code.Flickr blog, this is one of the cooler mashups I've seen.
The 'blind astrometry server' is a program which monitors the Astrometry group on Flickr, looking for new photos of the night sky. It then analyzes each photo, and from the unique star positions shown it figures out what part of the sky was photographed and what interesting planets, galaxies or nebulae are contained within. Not only does the photographer get a high-quality description of what’s in their photo, but the main Astrometry.net project gets a new image to add to its storehouse of knowledge.
The Flickr blog post interviews Christopher Stumm, who had the original idea to hook into the photo service.
Astrometry.net is creating "an astrometric calibration service to create correct, standards-compliant astrometric meta-data for every useful astronomical image ever taken, past and future...."