The price of peace is eternal vigilance.
The bots get smarter and we have to scramble to catch up. The captcha series of spam blocks has been defeated and it's been reported the Q and A is on its way out also. A human operator signs up and then cuts the bot loose.
A sure fire way to keep them under control is to have the new signups in a usergroup that has no hyperlinks, avatars, sigs, or access to PM/emails for say 10 or so posts (and the lobby doesn't count). By then staff should be able to figure out if it's legit or a spammer. Buzz did something like that at CV and it's working great.