Ice Cream Sandwich is now installed on 10 per cent of active Android devices, according to Google's own numbers. About 64 per cent of users are still using Gingerbread. And the latest iteration of Android, Jelly Bean, is already on its way.
When developers express concern about Android fragmentation, this is what they mean: users are distributed over so many different versions of the OS that it's hard to develop for a wide swath. Not to mention that the latest and greatest updates take forever to hit the masses. [Android.com via Business Insider]