I've installed SI Captcha yesterday, and everything seemed to be working fine at first, but a few friends who've tried to register informed me that they are not getting their confirmation e-mails with the password. I tried the process myself with addresses on two different servers, and I didn't get the confirmation mails either. What seems to be the problem? Are the spam filters filtering out the confirmation mails, or are they not being sent out at all?
I'll have to disable SI Captcha until this matter is resolved.
http://wordpress.org/extend/plugins/si-captcha-for-wordpress/