Does a Google Duplicate Content Penalty Exist?
Penalty is not exactly the correct word. What appears to happen is that in most cases your site is not rewarded with search engine love. The site that posts the original content first gets first dibs in search engine searches, which is how it should be.
But there are also other considerations. Take news sites for example. Most news based websites only offer duplicate content on their sites, yet they often have very good search engine rankings. One reason is their linking power and another is that they are constantly posting. Now, the type of information they post is what drives traffic to their website. So good traffic, solid links and continual updating, even if is duplicated content that is posted many times across the internet, seems to be Ok with Google.