Search Engines penalize duplicate content

I have read some articles regarding SEO and duplicate web contents. It seems like search enginese, espeically Google, will penalizes pages for having duplicate contents on it. The duplicate contents might come from other websites. Because Google keeps a large database of websites and it has smart algorithm, it can detect duplicate contents and penalize the pages.

So I guess to avoid being penalize, you should make sure your contents are not duplicates from other sites. Also make sure your pages are not dupliated from each other (make each pages at least 5-7% different from other pages on the same site).

There's a website called CopyScape.com (http://www.copyscape.com) that can help you the check duplication.