In this video, Matt Cutt’s from Google explains how duplicate content works on the web. He states that a huge amount of the web is duplicate content, and that is OK, however Google works hard to deliver unique content in their results.
Google tries to group content together and treat them as one piece of content. This is why it is so important to make pages unique for SEO, as it allows you to have multiple listings when before you would have only had one listing in the serps. Simple changes to titles, content and meta descriptions can make all the difference.
Cutt’s says that duplicate content is not spam, it is just something that happens and Google needs to deal with. While this is the case, he does state that in some cases, such as in the case of auto-generated content through an RSS feed, duplicate content could be seen as spam and Google reserves the right to take action on that.