A while ago I was getting idiot spammers creating accounts to post their stupid links. I then removed the automatic approval to admin approval. It was annoying to say the least. So then I just started banning them. So far so good. I haven't had any new users in a while.
To come to that kind of epiphany, one would need a brain capable of higher thought. I don't anticipate that happening any time in the near or distance future.
So I've retired a few of my security questions because the correct:incorrect ratio was too close and then added a new one. Also, the banning is doing pretty good still. Here's an update on that.