As Google announced the launch of its new Google Music service, the world’s largest search engine also revealed that the number of active Android devices has surpassed 200m.

And that number is growing rapidly, with Google now activating more than 550,000 devices each day.

As’s Lance Whitney notes, Google is on the tail of Apple, which has activated some 250m iOS devices. Obviously, the Apple and Google ecosystems are still quite different, but one thing is clear: Android is here to stay and in the smart phone market, is going to be more prolific than iOS.

But when it comes to operating systems, Google is finding that its success with Android isn’t easy to duplicate. The company had high hopes for Chrome OS, but DigiTimes is reporting paltry sales figures for Chome OS-based Chromebooks. In fact, according to DigiTimes, Acer, one of the hardware manufacturers that jumped on the Chromebook bandwagon, has sold less than 5,000 Chromebooks. And reports say Samsung, another Chromebook manufacturer, may have moved even fewer.

Google’s inability to find a market for Chrome OS isn’t all that surprising. I was one of many critics of the operating system, and noted that there were plenty of good reasons to believe it was destined for failure.

With 2012 shaping up to be the year of zippy, SSD-equipped ultrabooks, many of Chrome OS’ supposed advantages, such as fast boot up times, will mean very little, further dampening the prospects for Chromebooks and Chrome OS-based devices.

This really isn’t bad news for Google, however. The truth of the matter is that it doesn’t really need Chrome OS. Android has established itself in the market and has created significant opportunities for the search giant. At the same time, it’s not clear sailing for Google. There are plenty of challenges, from dealing with the Android patent situation to keeping hardware manufacturers happy post-Motorola Mobility acquisition.

Recognizing this, Google should take a lesson from its arch rival, Microsoft: one operating system is more than enough.