Ciro Cattuto wrote a simple piece of code that builds and visualizes a network of inferred semantic relations among the tags that Flickr users attach to their photos.
Using RhNav - Rhizome Navigation I wrote a data aggregator for Technorati's API. The first result is a video which visualizes blog domains by analysing Technorati's Cosmos (the blogs which link to a particular URL). The video is a screencast of RhNav fetc