Just found a lovely little Google Chrome add on called Graph Your Inbox throughMashable. They appear to take privacy seriously, and describe it thusly:
Graph Your Inbox is a Google Chrome extension that allows you to graph Gmail activity over time. You can use it to visualize your communication with friends, your Facebook activity, when you purchased items on Amazon or how often you use certain words or phrases. We provide the same search functionality used by Gmail, but instead of a list of messages we show you a graph of your email trends over time.
The examples I tried were doing a search on "from:facebook" and "from:twitter" and I got a lovely little graph showing me the number of conversations from each and when they occurred. Pretty cool; though I can't really see a serious use for it.
