Network mapping with Email

I think the tool that Cross talks about that tracks emails to map a network sounds absolutely fascinating. Thinking about my Gmail frequent contacts list and who I email often generally follows who I regularly meet with. Applying that concept of email mapping to work, in my case, it would show that I almost never contact certain coworkers that simply aren't useful to me (as harsh as that sounds). It also shows what coworkers in other areas of the company or organization are important to my work. This goes back to the informal networks that are frequently more useful than formal organizational charts and networks. To be able to map out those informal networks through this email tracking application just sounds amazing.