A few months ago I made a first stab which was take all the mail older than 6 months and go dump it in an archive folder. Today instead of reading some of those scientific papers I should've been working on, I (nearly) emptied my "personal", "work", and "unfiled" folders.
There was basically three fates: deletion, filing in archive, and getting marked as "todo".
I deleted all the spam, and unimportant mailing lists, and other miscellaneous events in the past. If the an email was just "for reference" it got dumped in archive. The result was about 26 emails which referred to something I should (still) be doing. I dealt with a few of them today, and now I only have 21 left.
Hopefully I can maintain this discipline--my old technique of leaving a couple thousand messages in one mailbox meant that those "todo" emails were pretty much lost once I'd gotten enough email to scroll them off my screen.