Origianally from a NYTimes.com article in 2005, I found reference to this recently on Adam Smith, Esq. (A free registration to NYTimes.com is required to view the full size image)

Some Computer Science professors analyzed one week of e-mail traffic from Enron (about 500,000 emails) in May 2001 looking for patterns that would help investigators narrow down their search. This infographic is the result showing the email connections between employees