Any experience regarding what % is considered duplicate?

[AdamThompson]

Some sites (including 1 or two I work with) have a legitimate reason to have duplicate content, such as product descriptions. One way to deal with duplicate content is to add other unique content to the page.

It would be helpful to have guidelines regarding what percentage of the content on a page should be unique. For example, if you have a page with 1,000 words of duplicate content, how many words of unique content should you add for the page to be considered OK?

I realize that a) Google will never reveal this and b) it probably varies a fair bit based on the particular website. However...

Does anyone have any experience in this area?

(Example: You added 300 words of unique content to all 250 pages on your site, that each had 100 words of duplicate content before, and that worked to improve your rankings.)

Any input would be appreciated!

Note: Just to be clear, I am NOT talking about "spinning" duplicate content to make it "unique". I am talking about adding unique content to a page that has legitimate duplicate content.

[AdoptionHelp]

Check out this video: http://www.seomoz.org/blog/whiteboard-friday-dealing-with-duplicate-content

It will give you a much more thorough answer than just a percentage of uniqueness. But if you want that kind of answer I mostly hear guesses between 20% - 40% unique content.