"This update is designed to reduce rankings for low-quality sites—sites which are low-value add for users, copy content from other websites or sites that are just not very useful. At the same time, it will provide better rankings for high-quality sites—sites with original content and information such as research, in-depth reports, thoughtful analysis and so on."
Google's announcement is a followup to what Matt Cutts stated in his blog just over a month ago:
"And we’re evaluating multiple changes that should help drive spam levels even lower, including one change that primarily affects sites that copy others’ content and sites with low levels of original content. We’ll continue to explore ways to reduce spam, including new ways for users to give more explicit feedback about spammy and low-quality sites.
As “pure webspam” has decreased over time, attention has shifted instead to “content farms,” which are sites with shallow or low-quality content. In 2010, we launched two major algorithmic changes focused on low-quality sites. Nonetheless, we hear the feedback from the web loud and clear: people are asking for even stronger action on content farms and sites that consist primarily of spammy or low-quality content."
Learn more information - http://www.webpronews.com/topnews/2011/02/25/google-finally-cracks-down-on-content-farms