Just wanted to throw out the suggestion that we need to have a "Dude, we have a problem with your content" notice on the backend plugin. A toggle on the Blogs -> Edit page would be good. Also maybe a banner across the front of the blog so folks won;t miss it (That was a common problem on wp.com) as well as maybe turn off rfc-xml access if that's been activated. (Again so they don;t miss it.)
Adding this to the antisplog plugin as a suggestion but may even work as a standalone.