From the post:
Using the GitHub API, Groovy and GraphViz to determine, interpret and render a graph of the relationships between GitHub users based on the watchers of their repositories. The end result can look something like this.
[Image omitted. I stared to embed the image but on the narrow scale of my blog, it just didn't look good. See the post for the full size version.]
A must see for all Groovy fans!
For an alternative, see:
Pointers to social graphs for GitHub using other tools appreciated!