CAPTCHA isn't a bad idea but even I dread when I need to do a verification since I can't read them half the time and I need to try a few times to generate one I can read. But I think it would slow down the spammers and let us see potential real forum users and not spammers.
I will look at see what needs to be done. This might need Thotter to look into.
Some addition info from the main site is below:http://www.captcha.net/
And modules for our base forum:http://custom.simplemachines.org/mods/index.php?action=search;basic_search=captcha
Possible scripting pages:http://www.phpcaptcha.org/