Over the past few evenings, set up WebUserPrefs on birdhouse hosting to allow users to configure their own SpamAssassin sensitivity thresholds as well as whitelists/blacklists. In the process, ended up contributing my bug fixes and new features back to both WebUserPrefs and the Communigate Pro plugin for it.
Birdhouse has deleted 84,982 spams for 40 mail users in the past 7 days alone. Now up to 98-99% spam blockage for users with filters on stun. One of our power users receives 13,000 spams per week to a single user account. The vast majority of them were to made-up names on the domain; rejecting mail to unknown names brought that down to around 1,000. Satisfying progress.