In a recent Blog Google Announced that they are going to change the rankings of smartphone search results, Google has earlier come up with the recommendation of building a ideal wap site also given common mistakes in smart phone sites.
The lasted changes in rankings of smartphone search results are based on the Google recommendation and common mistakes in smart phone sites
The most common mistakes are
Some websites use separate URLs to serve desktop and smartphone users. A faulty redirect is when a desktop page redirects smartphone users to an irrelevant page on the smartphone-optimized website. A typical example is when all pages on the desktop site redirect smartphone users to the homepage of the smartphone-optimized site.
You can read More about this at Google Official Blog