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If you go ahead, unfortunately, there's no warning from Google (in Webmaster Tools or elsewhere) about penalties. You'll sometimes see a message after the penalty is in place (but sometimes not at all). If it does happen, you can typically fix it, request re-consideration in Webmaster Tools, and within a few weeks to months, they'll lift it (presuming you've made the fix). That penalty/re-consideration process can be quite painful, though. In the event it happens, there's no long-term impact to PageRank/Authority/link metrics about the site. Best of luck, Rand