Official Google Webmaster Central Blog: Changes in rankings of smartphone search results

Webmaster level: Intermediate Smartphone users are a significant and fast growing segment of Internet users, and at Google we want them to experience the full richness of the web. As part of our efforts to improve the mobile web, we published our recommendations and the most common configuration mistakes.

http://googlewebmastercentral.blogspot.com/2013/06/changes-in-rankings-of-smartphone_11.html