For what it's worth, I second that request.
Let's face it, a lot of people don't want to register on every board they access, and I would prefer if visitors of my forum could choose not to.
But since we have been hit by Pepotamo the other day, I would also like to set up a threshold for spammers without harassing regular visitors.
Registered users should not need to visually confirm their posts, of course, just Guests.
Plus, the visual confirmation code already is included, so it should be fairly easy to implement (sorry if this is an incorrect assumption, I can't code at all