What does this do? Well, it may help you change your email habits by showing your patterns.
The link from LifeHacker is here
You create a new spreadsheet in Google Docs, name it Gmail Meter and then run a script from the Script Gallery.
Then let the script run. It can take a while to run but you can just let it go, it will send you an email when it's done with all of the stats. What kind of stats? Here's just a smattering of the stats: