I'm tempted to see what my email volume looks like since starting Product Hunt (because most of my day is tweeting and emailing) but I'm hesitant to give them access to all of my email. I'd be fine if they could only read email headers.
I enjoyed the data-nerd novelty of this info for a few days, and then forgot about it. But beware: months later, I've started getting daily script-failure emails from google apps saying "Summary of failures for Google Apps Script: Gmail Meter", and I just can't get them to go away!
Same as Ryan, I'm hoping the baseline stats help my improve my performance with email. Using for a month or so now, I'm finding it useful to see the response times decreasing as I become aware of them.
I haven't found the total number of emails or the ranking of most frequent contacts to/from as useful as I thought, as it doesn't correspond much to something I can adjust or that would have benefit of being a strategy.
Total length of emails is something I'm happy to see and track, as downtrending on that helps gain me more time back for other tasks. But again, mostly I'm just finding value in the time-to-respond metrics, and even then I might drop the tool off in a few months as I won't require it ongoing. It's been great though getting visibility on the macro trends in the meantime.
Product Hunt
Email Meter
Corilla
Cascadeur