I find the following four resources fine for duplicate content.
blogspot.ro/2008/09/ demystifying-duplicate- content-penalty.html
blogspot.ro/2009/06/traffic- drops-and-site-architecture_ 29.html
- Don’t create multiple pages, subdomains, or domains with substantially duplicate content.
- Avoid… “cookie cutter” approaches such as affiliate programs with little or no original content.
- If your site participates in an affiliate program, make sure that your site adds value. Provide unique and relevant content that gives users a reason to visit your site first.
- If you’re a webmaster of beginner-to-intermediate savviness, you probably don’t need to put too much energy into worrying about duplicate content, since most search engines have ways of handling it.
- We recently launched a redesigned document-level classifier that makes it harder for spammy on-page content to rank highly. The new classifier is better at detecting spam on individual web pages, e.g., repeated spammy words—the sort of phrases you tend to see in junky, automated, self-promoting blog comments.
- Original and compelling content is crucial for a good user experience. If your website participates in affiliate programs, it’s essential to consider whether the same content is available in many other places on the web. Affiliate sites with little or no original and compelling content are not likely to rank well in Google search results, but including affiliate links within the context of original and compelling content isn’t in itself the sort of thing that leads to traffic drops.
- … make good use of the rel=”canonical” attribute to reduce the indexing of duplicate content on your domain. The example in the presentation shows how using this attribute helps Google understand that a duplicate can be clustered with the canonical and that the original, or canonical, page should be indexed.
Note: Also see the Yahoo! Group on which I present similar issues:IMRo. To join, email email@example.com and reply to the confirmation email.