I've been approving the new members manually. I don't approve anyone with a suspicious email address. That means if I don't recognize the email server, such as yahoo, gmail, etc. you don't get approved.
I'm also not approving anyone that did not put thought into their user name, and it makes no sense, are rejected.
Likewise rejected are those that are advertising a product in their user name. So goodby, Mr. Porn-links.