In a recent Tweet, the Android Master himself, Andy Rubin, Tweeted that the number of Android activations per day has increased to 500,000. During Google I/O the number of activations were at 400,000 per day, which means they've grown quite a bit in just one month, and from the way it appears, that growth isn't slowing down at all yet. Furthermore, with the push of new Android devices coming this year, and the promise of Android 4.0, and it's big marketing exclusive device halo just around the corner, it's entirely possible that the Android growth world-wide hasn't even peaked yet.
Source: Google/Android - Andy Rubin Tweet