QUOTE(dagnyjbarber @ Oct 1 2012, 11:26 AM)
Duplicate content generally refers to substantive blocks of content within or across domains that either completely match other content or are appreciably similar. Most of the time when we see this, it's unintentional or at least not malicious in origin: forums that generate both regular and stripped-down mobile-targeted pages, store items shown (and -- worse yet -- linked) via multiple distinct URLs, and so on. In some cases, content is duplicated across domains in an attempt to manipulate search engine rankings or garner more traffic via popular or long-tail queries.
After Google penguin update it detected duplicate content of sites, due to that reason it dropped their rankings, page rank and Google has penalized those sites as well.