How do I get SpamAssassin to run faster?

Use [http://www.spamassassin.org/full/3.0.x/dist/spamd/README spamd].

Ensure you are not using a locale that uses UTF-8; UTF-8 character sets have higher overhead for text-processing applications: Utf8Performance

If you are using network tests, install a local DNS server (BIND named, for example) on the same host to cache responses, and set the /etc/resolv.conf file to use that instead of one on another machine.

Consider turning off network tests, and running with "-L", if you can afford a drop in accuracy. (This is not a very good option for most people though.)