A team of three students in the Sociable Media Group at the MIT Media Laboratory - Fernanda Viégas, Scott Golder, and Shreyes Seshasai - have built an application called "Themail" to visualize the contents of an email archive.
"Themail" helps you see the words that keep popping up in your conversations. It also helps you to see how your conversations with one person may differ from the rest.
I liked the visualization of the emails over time. If you use Gmail and it's loaded with emails, this gives you a real sense of of the threads of content and people through time.
Give it a try and play with clicking on key words to see their connections.