The announcement from Yahoo!, Live & Google that they will be supporting a new "canonical url tag" to help webmasters and site owners eliminate self-created duplicate content in the index is, in my opinion, the biggest change to SEO best practices since the emergence of Sitemaps. It's rare that we cover search engine announcements or "news items" here on SEOmoz, as this blog is devoted more towards tactics than breaking headlines, but this certainly demands attention and requires quick education.
Canonical URL's for WordPress
As described in this post, this plugin adds rel="canonical" links to your blogs
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