Ok, I know that AdSense stats are not truly accurate in determining smart phones however May 2014 AdSense showed for me more than a quarter were tablet/smart phone earnings. This is interesting since even only two years ago my tablet/mobile earnings were not even 10%, since then:
2013 Jan-June 16.6%
2013 July-Dec 22.1%
2014 Jan-May 24.8%
2014 May 27.7%
Are you seeing similar/higher/lower ratios?