Some time ago I wrote about how I manage the flow of email hitting me. Back then I didn't talk about what happens to the email after it's been filtered and automatically sorted.
Here's a quick picture of my email folders:
POPFile does the automatic sorting into the sub-folders when I download mail (read the article linked above for details on that) and I then manually move mail that I can't respond to immediately to the ACTION folder (to make this quick I use the lovely TB QuickMove Extension which makes all my mail moving a CTRL-# click away).
Anything that's in ACTION needs to be dealt with. Sometimes that means those messages will be gone in a day, sometimes in weeks, just depends on the contents. There are also a couple of other 'action' type folders called Next Newsletter (where I store interesting stuff to mention in my next spam and anti-spam newsletter) and Next GNU Make (where I store stuff that'll go into next month's CM Basics Mr Make column).
It occurred to me that the depth of my inbox might be an interesting thing to track so I wrote a quick Perl script that parses the mbox file associated with the ACTION folder looking for non-deleted messages (I look at the X-Mozilla-Status header and check that the 0x8 bit is not set) to get a count of the messages in ACTION.
Then I pump that data into rrdtool using the RRD::Simple interface from CPAN and use it to create graphs of the number of waiting items. All this runs off a cron job every five minutes (and once an hour for graph creation).
You can see the 'live' graphs here (these will update hourly when my machine is on):