It is imperative that you do not use duplicate content. You cannot copy something even if you wrote it if it appears on a different site on the web. For example if you wrote a blog on myspace you can not take that same blog and put it on an article site without removing it from myspace first. If you do this, this article will be considered duplicate content and Google will shun it from rankings and traffic. You want to Avoiding duplicate content at all costs! Google is in the market for fresh and new content pages so you have to always have new content. Duplicate content is a big no no!