We discussed CAPTCHA Friday in CSC.
I would think the modern spam company can easily break a CAPTCHA code by simply copying the image, relaying it back to their site, requiring a user to answer it to access the spammer's site, then, possibly equipped with the correct code, the bot would return to the original form.
However, I think it'd be more beneficial now, to allow everyone (registered, unregistered, bots, etc.) to VIEW the forums, however remove 'guest posting' in it's entirety so that more users will be registered users, of whom we can tie a static name to, and keep on an eye better.
-y00tz