Re: duplicate content
Even though this is the Adwords Forum. I will answer your question.
Search Engines frown upon Duplicate content. When pages and sites are duplicate, Google / search engines typically will only index the potential original, and not index the others.
Also in the mix are google filters such as Penguin and Panda, that look for both Quality factors as well as bad linking habits.
20% duplicate would be still considered bad, especially if it is copied material from other higher valued websites. Strive to have the least amount of duplicate content as possible. Now there will potentially always be some variant of duplication as navigation or coded themes may contain the same variables.
When looking at duplicate content, it's not just the text on the page ( main issue) but also the code. If you mirror your website and change just a few lines, the mirrored site could also be considered duplicate content.
Use copyscape as one method to check duplication, the other is to check your pages with an actual live search in Google. Follow these steps
1) Open up one of your pages in a browser
2) Pick a 7-10 word phrase from your written text.
3) Copy that phrase and open another window or tab
4) Go to Google. Paste that 7-10 word phrase as a search query and add quotes before and after your phrase text. Hit enter - Example in google search - search for "7-10 word phrase"
5) Look at the result. If your site comes up #1 for that 7-10 phrase then you page is considered the original and fine. If your site doesn't come up, or is 5-6 ranked or even lower. then you should consider rewriting the content on that page.
Do the search several times for different phrases and different pages. To see if you are in good or bad with the search engines of your choice.
If you can't rank for a "7-10 word phrase on your website in quotes" as a search query, then you have issues with SEO and will not rank for normal topics you would expect people to search for an find your site.