Punitive Actions:
If you find a spammer has made it past your 4 front-lines of defense, and has managed to post on your forum, then you can help the community...
The spammer's details can be sent to the Stop Forum Spam and Akismet databases automatically, preventing them from registering or posting on other forums. When other forums do the same, the protection is reciprocated.
Simply moderate a post and choose the option to "Delete Posts As Spam..." an then choose the option to "Ban User." Banning the user sends their details to either Akismet, StopForumSpam, (or both) depending on how you set it up.