One thing you notice if you get involved in a lot of the online marketing forums is that there is a lot of confusion about duplicate content and its ramifications for webmasters, bloggers and article writers and marketers.
Many people seem to think that they will be penalized if they submit the same article, say, to several directories. They fear that their site may be delisted from search engine results. But this is not the case. It just means that Google will find what it thinks is the original article (that is, the one that was indexed first - probably the one at the article directory it was submitted to first, particularly if that's a high page rank directory) while filtering out the copies.
The penalty only really kicks in if you have duplicate sites.
Here's a good clear article describing this distinction in much greater detail.