Google's mobile search volumes doubled Y-o-Y in December 2011

"Google’s lead product manager for mobile search ads, Surojit Chatterjee, tells us that in December 2011 mobile search ad request volume was more than twice as high as it was in December 2010. Mobile search in general has grown five-fold worldwide in just the past two years, which is a rate comparable to the early days of desktop Google Search, he adds.
Chatterjee says that quality of search ads is increasing thanks to some of the new factors being considered in mobile search ad rankings. For example, mobile web-optimized sites are now ranked higher. Since August 2011, Google has seen more than a 50 percent increase in the number of AdWords advertisers with a mobile optimized sites."

Source:  TechCrunch, 1st February 2012