Using Stop Spammer Registrations greatly reduced the spam that did get through before. Coupling this with Limit Login Attempts has made my life easier dealing with spammer registrations and brute force attacks.
I have been using it for awhile and I find myself checking the stats every once in awhile because I don't see any spammers. I almost wonder if they are not trying to attack, and then I see the stats. Amazed at how many some of my sites get (unsuccessful) attempts.
I just wish WP itself would log the IP on a successful registration and I am amazed that it does not. This is a shortcoming with WP and not with the plugin.
This is one of the must have plugins for clients and myself.