Here's a pretty in depth explanation of SpamAssassin. All of it's triggers and the explanations of such and how to fix. I've referenced it a few times. Might be helpful to some who are less tech/coding savvy. http://help.campaignmonitor.com/topic.aspx?t=104
Good stuff Chappy...I had this link saved from way back... http://spamassassin.apache.org/tests_3_1_x.html