Each day, more than half a million Android devices fire up. That's the word from Andy Rubin, Google's VP of engineering. In a Twitter post Monday, Rubin also noted the number of Android daily activations is growing 4.4 percent week over week. It was only two months ago that Google touted daily activations at 400,000. If Android maintains this growth rate, the activations will double again -- to one million -- by the end of the year. While that pace will likely level off, the daily activations give Google a dominant position among smartphone operating systems.