This module is able to generate a network (directed graph) from the users activity on the site.
Several operation (shortest route searching, clustering coefficient, strongly connected components, distribution of edges) is implemented on this network. The module has very resource-consuming parts so in a huge site you have to test the performance.
The map of your sites network can be generated by graphviz (the proper input is generated by the module) and a graph visualization applet iincluded in the module's package.
The full package can be downloaded from http://sna.drupaler.net. The CVS version doesn't contain the network visualization applet.