If you want to have your photo (potentially) show up beside your site's results on Google.

UNdata provides a catalog of 27 United Nations statistical databases and 60 million records about the past, present, and future state of the world. Topics include demographics, life expectancy, labor levels, poverty, and a lot more.

How do you implement full-text search for that 10+ million row table, keep up with the load, and stay relevant? Sphinx is good at those kinds of riddles.

Face finding/face detection

Upload an image and find similar images on the web