• Double posting — Most forums have a rule against this, but it still happens.  Sometimes it’s allowed in a certain forum (like the sandbox on my forums), or allowed a certain period of time after the previous post was made.
• Bumping up old topics — Most forums have a problem with this.  It is simply not socially acceptable to bring up a conversation from 2001 that hasn’t been posted on since then.
• One-word posting — “lol” is not an acceptable post on any forum I know of.  It would be pretty simple to block posts with no spaces in them, and also have a minimum character count per post.

I’ve decided to make a plugin for bbPress that blocks the three types of human-generated spam I just listed.  If anyone has any ideas on other things I could block with the plugin, please tell me here.

Edit:

I have completed the development of Automated Forum Moderation’s first release.