Some info about Google duplicate content

"I'd agree with most of your video and your bullet points, but lean more toward Michael's viewpoint on bullet point #2; duplicate content doesn't make you more likely to have pages in the supplemental index in my experience. It could be a symptom but not a cause, e.g. lots of duplicate content implies lots of pages, and potentially less PageRank for each of those pages. So trying to surface an entire large catalog of pages would mean less PageRank for each page, which could lead to those pages being less likely to be included in our main web index. I'm not aware of an explicit mechanism whereby duplicate content is more likely to be in our supplemental results, but I'm also happy to admit that as supplemental results are different from webspam, I'm not the expert at Google on every aspect of supplemental results.”

From: http://www.seomoz.org/blog/whiteboard-friday-supplementary-my-dear-watson