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Meta-keywords in the head of pages have no SEO value, and in some instances may even be used as spam signals. It's been a very long time since they ever had any value. So Drupal did the right thing by removing them by default. I understand there may be a few smaller European search engines that might still use meta-keywords, and there are some internal site search engines that use them for internal indexing purposes. But if neither of those cases applies, there's no point in wasting any time implementing them. Hope that helps? Paul