Integrated the forum with a spam abuse service.
People registering with IP addresses and email addresses that have been previously flagged as spam by other websites will be stopped in their tracks. Lets hope this significantly reduced forum spam. Its already stopped its first SPAM sign up.
Update - looks like over 95% of the spam is being stopped in it's tracks now. Only spam accounts registered long ago are getting through. Hang gliding forums without all the spam allow me to focus on better things.