Ten years and about 50,000 inbox e-mails later, it's pretty obvious to me that smart filters have a vital role to play.
Hah. I just checked my email inbox. It goes back to February 7, 2007 -- 168 days. It contains no spam, and almost no newsletter type email -- I delete all that stuff. I have 14,145 items in there, an average of 84 per day.