A while back I wrote about Marc Smith, Sociologist at Microsoft Research who is studying Usenet Newsgroups. I met and saw a presentation by Marc recently and I've been keeping up with NetScan- the tool they use to analyze newsgroups. I've been impressed with some of the ways they are graphically representing the growth and activity of the newsgroups over time. The screenshot below came from this TreeMap.
It looks incredibly complex, but once you read the key, and view the whole thing, it becomes a really interesting representation of the changes in the newsgroups- particularly over time.
Also, the site has a dynamic representation of cross-posting in the newsgroups. Again, see the instructions to manipulate the graphic.