If you and gmail go back a ways, MIT have created a very interesting online tool. Immersion can show you who you communicated with, at what times, who introduced you to whom and how your various contacts are interrelated. Data is displayed as a web of connections, and clicking on the individual nodes/people drills down into their specific statistics. MIT do not scrape your email content, just the from, to, CC and timestamp fields, and that seems to be enough to generate some fascinating information.
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