[Hampshire] Spamassassin and DKIM/Domain Keys

Is anyone using Spamassassin to check DKIM/Domain Keys on incoming mail?
I've set up a test environment with the SA DKIM plugin, but none of the
incoming mail (with valid DKIM, invalid DKIM or no DKIM) is identified by
SA as having a DKIM problem. I'm also unable to find any information on
setting up SA with DKIM. Can anyone provide any pointers?

Thanks,
Keith