Handling spammers after registration?

We use FaceBook and Google connect for user registration and blog creation on our MultiSite environment . So I think that we need not worry about Spam registrations. It slow downs spam registrations .However I believe , there is a chance to spam after registration . How can I use your plugin useful in that way ( Handle the spammers after registration) .

Do you think there is much chance of spam, even I use FaceBook and google Connect methods?

Thank you!