I regret doing this, but the spam is getting to be too much of a pain in the butt. I've adjusted the security settings so that only registered users may post on P.Planet.
Perhaps doing this will cause the spammers to go away, and then I can switch back to allow any visitor to post.
I've been reluctant to set it up this way because I know that many people visit and only become members once they feel comfortable and at home around the tribe.
So let's see how it goes, eh?
If there's a big problem, I can change it back easy enough.