I've turned up greylisting (using milter-greylist) on the geeklair.net mailserver.
This anti-spam measure should reduce the number of spam/virus emails that get delivered (so the volume of mail that needs to go through spamassassin and clamav is smaller).
The downside is that it makes mail delivery take a little longer (which could be especially annoying in the case of password-reminder or order confirmation emails). I've turned the amount of delay that milter-greylist needs way down, but the total delay is dependent on the sending mailserver.
I think the tradeoff is reasonable. As always, let me know if you notice any problems or have any concerns.