Let's imagine you've written a book about pottery, and to promote it, you publish a pottery blog. Last year on your blog, you wrote a nifty tutorial on fixing broken pottery. Word has gotten around, and now every pottery site on the Internet links to your pottery-repair page. Because of all these links, your page is the top Google result for "repairing pottery," "fixing pottery," and several related queries. That single page is your Web site's crown jewel, accounting for half your new visitors and a good portion of your book sales.
Now let's imagine you try to squeeze even more traffic from your pottery-repair article. You post it to EzineArticles.com, without changing much except to add the links back to your site. Meanwhile, you upload the same article to other syndication sites like GoArticles.com and IdeaMarketers.com.
Now you sit back and wait for the extra traffic, but the exact opposite happens--you see less traffic, not more. Now that your article appears on a bigger, more popular site, it's likely that Google will send searchers there instead of sending them to your site. Google has made a quick calculation of which site is more authoritative, and because EzineArticles.com has more links than your site, it wins. Google doesn't care that you wrote the article and have the Internet's best pottery site.
The lesson is, keep your most valuable content on your site exclusively. And if you're going to syndicate existing content, rewrite it substantially so the search engines don't penalize you for it.
Google's Adam Lasnik, the company's "search evangelist," offers two tips for avoiding the duplicate content penalty:
If you syndicate an article containing the same or very similar language that appears somewhere on your site, ensure the syndicated article includes a link back to the original article on your site. Don't include only a link to your home page or some other page.
Minimize boilerplate language on all your content. For example, instead of including lengthy copyright notices at the bottom of all your Web pages, include a brief summary with a link to a page containing your full copyright notice.
None of these safeguards, however, is foolproof. The only sure way to avoid the duplicate content penalty is by syndicating original material only, and keeping your best material exclusive to your site.