Matt Mullenweg has written the following blog post, Email Load http://ma.tt/2010/09/email-load/ :
I added a new feature to the contact page that shows you how high (or low) my email queues are, which update once a minute. If the levels are lower, it probably means I’ll get back to your sooner.
You can see it in action on his contact page:
This idea has the potential to be a good add-on for GF, particularly if it more effectively conveyed the basic idea - that you are busy and might not be able to reply promptly - by rendering the numbers as a chart, using colors to denote how overheated each section is.
I particularly like the fact that it indicates priority but I wonder if using the phrase "Low priority" might seem dismissive to someone who is anxious about whether or not you will reply to them. Might be better to number High Priority or Urgent emails, then Everything Else.
Matt's version pulls the numbers from his email server but, as a GF add-on, it would have truly mass appeal if it could pull the same sort of info from a specified GMail or Google Apps account. It would be particularly good if it could hook into Google's superb new Priority Inbox feature.