We’ve had some discussions about fighting scraped content (aka Plagiarism, aka stolen content, AKA scrapper sites, AKA duplicate content) on Mahalo recently. Our team recently put together a best practice for this with a tool and a short video today: http://greenhouse.mahalo.com/Plagiarism_Tool
You can never beat all the stolen/scraped content out there, but we can certainly do a better job than machine search engines.