SEO: There Is No Duplicate Content Penalty

Google has long though to penalize websites that duplicate content or produce material that is more or less the same as other websites. This Duplicate Content Penalty is a myth. What happens instead is there is a lessening of pagerank and authority that goes to a page, when the search engine spiders see incoming links to the same page as different URL’s.

There are many causes of content duplication. When tracking features are appended, filtering and sorting options append parameters to the URL, a site does not link consistently by subdomain, print versions generate a new URL, etc, duplication can occur. Home pages are a prime example; while the domain resolves as the home page, clicking on any navigational links to the home page takes you to a different URL.

A lack of canonicalization can also cause duplication of content. 301 redirects are the best way to canonicalize duplicate content, deindex the matching links and consolidate link popularity. Cannibalization occurs when two or more pages from the same site target a single keyword. 301 redirects cannot help you on this one so you can try distinguishing the content so it targets different keyword themes or using a canonical tag which would be used to recommend consolidation of link popularity without redirecting the user.
By using 301 redirects and canonical tags and little common sense, you can easily avoid duplicate content and improve your SEO.