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It's a complicated issue, but adding 50K variations to 27K product pages can definitely be dangerous, especially post-Panda. At best, you're diluting your index and your ranking ability. At worst, Google could actually start de-indexing or at least devaluing core pages. Personally, I don't think the long-tail gains are worth the risk - these kinds of pages were behind the "May Day" update in 2010, and Panda continued that core philosophy. Google considers it a low-value tactic in 2012 - of that, I have no doubt at all. Of course, it does depend on how you use them. To have custom landers for PPC and not index them is perfectly fine, for example. If you're tripling your indexed page count with thin content just to target SEO keywords, though, you're taking a very real risk, IMO.