Google is constantly fine tuning its algorithms to prevent spam and increase the quality of search results. In most cases, few outside of the search engine marketing industry even notice when Google makes a change. Earlier this week however, Google started rolling out an algorithmic improvement to US users that will have a noticeable impact. This update may prove to be the most significant single update in years. According to Google's recent blog post post 11.8% of queries will be impacted. Some Webmasters are already reporting issues.
"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."