A useful post and advice from Google how to handle duplicate content:
John also goes on to say some good advice about how to handle duplicate content on your own site:
- Recognize duplicate content on your website.
- Determine your preferred URLs.
- Be consistent within your website.
- Apply 301 permanent redirects where necessary and possible.
- Implement the rel=”canonical” link element on your pages where you can. (Note – Soon we’ll be able to use the Canonical Tag accross multiple sites/domains too.)
- Use the URL parameter handling tool in Google Webmaster Tools where possible.
They have not updated their webmaster guidelines on duplicate content as yet.
Consider blocking pages from indexing: Rather than letting Google’s algorithms determine the “best” version of a document, you may wish to help guide us to your preferred version. For instance, if you don’t want us to index the printer versions of your site’s articles, disallow those directories or make use of regular expressions in your robots.txt file. Google
Here’s some recent official Google advice for duplicate content accross multiple sites (and some internal advice):