Recently, Google did a major update to it's search engine algorithms at Thursday, February 24, 2011 last week. This is done to get rid of web content farms and low quality websites from it's SERPs (Search Engine Result Pages). But this new change only first applied in the United States.
Google's actually doing a lot of small updates regularly to improve the quality and performance of it's search engine. Those updates mostly not recognized by most users. However, for a big update, Google usually announce and explain the impact of such change.
This time, Google expanded it's battle to fight against web content farms and low quality sites such as web site with lots of ads and a lot of pages but little content, and websites that mostly just take content from others with few to none original content.
Google explained that with this change, (hopefully) all low quality websites will go down in rankings and high quality website will get better rankings. But, it did not explain in detail how a website would be considered as high quality and worthy to be placed on a higher ranking.
According to Google, a quality website is a website that contains the original content (not copy from somewhere else) and has detailed information. It's as said by Amit Singhal and Matt Cutts on Google's official blog, "Google 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."
Surely, this change will affect the SERPs to approximately 12% of total searches on Google. These significant changes will be rolled out soon in other countries after the pilot project in the United States.
For those of you who have a website, go check and modify your website to make it more interesting and useful for people. Also you must avoid copy and paste articles and posts from other websites and just write your own article. That way, Google will be your best friend.