Good stuff has been said, but my perspective is to treat them like lying children, instead of taking pro-active action against them. Just let everyone know about them, post responses which indicate plagiarism, and recommend people don't answer them and downvote them.
in reply to How should Perlmonks deal with Plagiarism?
I mean, why get so upset over it? Do you want to get an ulcer by constantly watching their posts then digging for the plagiarized source?
I propose actively ignoring them, and hope they go away. If they know they can agitate us, they will. And that could get ugly if they sign up for a bunch of phony accounts and just start plastering the nodes with junk..... then the janitors will be forced to take very undemocratic action, like summarily deleting nodes.