In February 2011, Google changed its search alogorithm in an attempt to reduce the number of content farms and link farms that show up in its search results. The effort has been largely successful in reducing content farms in search results.
In addition, Google added a feature to search that allows you to block certain websites from your results. Follow the instructions to the right to block a site.
1. Do a Google search.
2. Click on an article or website link.
3. If you recognize the website as a content farm, click back to Google.
4. There will now be a link that allows you to block all results from that site.
5. Click the Block link, and all results from that website will be removed from your search results.
Source: jongales.com