I was spammed (500 new users per hour) until I added the CAPTCHA. The captcha works great, but now (guessing because my site is a PR5) I get useless posts daily (directories, cell phone accessories) that I have to clean out.
So for me, CAPTCHA stops the bots, but the lazy
SEO kiddies looking for a quick link get be the CAPTCHA. So, the verification email will hopefully be one more step to block unwanted posts.