Google makes an algorithm change on May 2010. This change in Google algorithm is coined by Webmaster World as “Mayday” update.
Matt cutts said that this change would affect long tail keyword ranking. Low quality sites getting traffic through long queries will find a sharp dip in their traffic. High quality sites asusual thrives and remain unaffected by the “Mayday” update.
Inner pages of large websites without value added content and backlinks are the worst affected ones. We find lot of dynamic websites ranking for inner pages having very less content / no content. These kind of pages ranking well for long tail keywords gets the beating from Google's ranking stick.
By making such an update Google consistently works towards providing high quality results to it users world wide. There is no wonder why people prefer using Google to find the products / servcies / information / anything they are looking for. Every one who uses Google gets the relevant high quality results they are looking for.
It might not be a good news for SEOs who toil hard to promote their client websites which is not having a high quality in the eyes of Google. But nevertheless it is job of ethical SEOs to improve the quality of websites they SEO.