Jelly Bean now on 25% of Android devices
4.2.x. But 39.8% of Android users are still powered by Gingerbread with 39.7% holding a model running Android 2.3.3 to Android 2.3.7. So the majority of Android devices are still being driven by a 30 month old build. Right behind them is Ice Cream Sandwich users with 29.3% of Android devices.
By next month, we could see Jelly Bean take over second place from Ice Cream Sandwich, but it is going to take some more time before enough Gingerbread users upgrade to a new phone to change which Android OS build is at top.
source: Google, AndroidDeveloper