Google is changing the way they handle search returns for mobile searches. And in their Webmaster Central Blog, they spell out two of the most common mistakes webmasters make, faulty redirects and smartphone-only errors. If webmasters make these mistakes, they're going to be hurt in the mobile search results. Webmaster need to head over to this Google blog entry to make sure they're doing things correctly.
http://googlewebmastercentral.blogspot.com/2013/06/changes-in-rankings-of-smartphone_11.html