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I'm wondering though, say if I were to republish legal content from maybe 50 different sites and combine them with some original articles, would there be a penalty for duplicate content, and if so, how serious?
That way you'll be able to put this problem behind you. I don't see how anyone could really give you a hard and fast answer about what will happen, or how much duplicated content is too much.
(BTW, per your other thread, you can ban Googlebot while still allowing the AdSense "Mediapartners" spider. I doubt that would involve any risk.)
Here's where you can grab database dumps:
Here's where you can export a few pages at a time: