Mobile ad network AdMob has just released its latest stats tracking the rise of Android, and it's clear that Google's mobile platform is quickly gaining steam. AdMob writes that between October and December, the number of ad requests worldwide from Android devices increased a whopping 97% to over 1 billion ad requests. In other words, the number of Android devices doubled in just two months. Much of the growth was clearly driven by the release of the Motorola Droid . Before the Droid's launch, HTC devices accounted for 98% of Android requests. In December, that fell to 56%, with 39% from Motorola (which also offers the CLIQ) and 5% from Samsung.