I have added a new hidden option, 'captcha_member_days', for setting a number of extra days CAPTCHA will run for for new members.
This should reduce the chance of a member joining then going on a spam spree.

Also 'captcha_member_posts', for the number of forum posts they need to make until CAPTCHA goes.

These should be made official options.

The probation usergroup by default should not have the privilege discussed in this topic. OR, the documentation talking about the antispam_question technique should suggest to remove that privilege.