Expand GmailZero to count the average time it takes to respond to email
This would be valuable in putting the focus on (finally) handling all those older emails - the ones being postponed for too long - that linger in the inbox.
Another option - which would perhaps be easier to implement - would be to calculate the average age of the remaining emails in the inbox.
Christopher Allen commented
Not quite what you want, but a possible alternative in the meantime: create a Gmail goal for "in:inbox older_than:2d" (or similar).
Admindreeves (Cofounder, Beeminder) commented
Wow, this is smart; I can't believe I never thought of this metric. It sounds like a great way to plug the loophole I've found for my gmailzero goal, which is to use my nifty gmail snooze script -- http://messymatters.com/snooze -- to keep snoozing messages I'm procrastinating on.
I wonder if the metric should be the sum of the ages of all the messages in your inbox, so it's like minding message count weighted by age. (A problem with that number is that it isn't prima facie meaningful.)