Greg Grothaus of Google explains very well Google’s philosophy of duplicate content. They realize that a lot of duplicate content is not manipulative but simply webmasters trying to take the same content and make is useful in different formats.

For example, if you have content on a page about “10 tips on package fragile glass for your move”, and want to include it in print format as well. Google doesn’t penalize you for the duplicate content. They just include one of the sources and not the other. We’ve been telling our clients for a long time that Google doesn’t penalize duplicate like people think, it’s nice hearing the explanation to how and why they even recognize it. Spam on the other hand, they attach pretty aggressively.

Greg then shares a simple explanation on how to prevent issues that may arise by utilizing the 301 redirect and the new rel= “canonical” tag. I highly recommend viewing the information directly from the horses (Googles) mouth.