" Flickr Graph is an application that explores the social relationships inside flickr.com. It makes use of the classic attraction-repulsion algorithm for graphs."
This is really quite wild. You click on any node, and it becomes the center of the graph with all relationships dynamically linked. I'm not sure exactly how I'd use this ... or when I'd find time to use it ... but this is cool.
Here's an image of the tool from cogdogblog, and try it out yourself at http://www.marumushi.com/apps/flickrgraph/flickrgraph.cfm?q=willrich