On a new site with a bbpress forum, and using "New User Approve" on the first day I got over 100 spam user registration requests.
Installed and configured Stop Spammers with all the API keys and not a single spam request came through. The really good news is that several legitimate users were able to register.
As an added measure of security, I put up a Wordfence as well.
The combination of New User Approve, Stop Spammers, and Wordfence has allowed me do something else with my life other than weed through spam trash.
With Wordfence it is so cool and so easy to identify "bots that don't belong" and block them. That and the automatic detection and blocking of "snoopers" is absolutely fantastic!
love it, love it, love it!