In a posting on Official Google Webmaster Central Blog, Webmaster Trends Analyst Susan Moskwa reiterated that Google Search does not have duplicate content penalty. The theoretical penalty refers to being penalized in the Google search engine due to a site having multiple pages containing the same content. This can be a common occurrence, among the causes is a dynamic site that uses multiple URL parameters. The issue has been addressed in several previous postings on the Webmaster Central blog, but continues to be concern to webmasters. When Google does find duplicate content, it clusters the duplicate contents properties together, including link popularity, and attempts to choose the “best” URL to represent the content in search results. If Google is unable to detect all the duplicates of a page, the page’s ranking may suffer to due not receiving the link popularity of all the versions. The post suggests using a Sitemap to help Google understand what is the preferred URL.
In a posting on Official Google Webmaster Central Blog, Webmaster Central