Daniel Bogan, known as Waferbaby (whether he's a nerd, Catholic, or a Catholic nerd is left unclear), created this mesmerizing visualization of Flickr.com, Yahoo's excellent and immensely popular image uploading service. Thanks to Gizmodo for finding this little gem:
To create this, he used Gource, hosted here on Google. Gource's visualizations are based on the structure of a tree--the root directory is, coincidentally enough, the "roots," with other directories appearing as "branches" and files as "leaves." So when you see a huge new splinter in the video, that might mean a new feature was introduced, along with all its accompanying source code. Is it useful? Not particularly. Pretty? Absolutely, yes.