Android 4.0, otherwise known as Ice Cream Sandwich, was released last fall. More than eight months later, it's migrated to just 11% of Android devices. The real figure may actually be a little lower; Google's numbers are based on Android devices that connected to the Play store over the past two weeks. Android 2.3 Gingerbread was by far the most popular, garnering 64% of the pie. Less than 2.5% of users were on Honeycomb, the tablet-focused Android 3.x release.
The slow adoption of Android 4.0 doesn't give us much hope that version 4.1, a.k.a. Jelly Bean, will be picked up en masse. Google is trying to ease the upgrade process for hardware makers, though. At the I/O conference last week, it announced that a Platform Developer kit will be available to device makers 2-3 months before new versions of the OS are released. A "beta PDK" for Jelly Bean has been circulating among hardware vendors for a few weeks already.
The problem, of course, is that all those folks want their Android devices to be unique. Most hardware makers drape their own skins over the UI and incorporate their own features into the OS. Those tweaks must be ported to new versions of Android, and having early access to the code should speed the process.
Some Android flavors are more heavily customized than others, and you can probably tell who's doing more fiddling under the hood by how quickly Android updates are released. Asus doesn't mess around too much with the OS, and its tablets were among the first to be upgraded to version 4.0. The TouchWiz-infused Samsung Galaxy Tab, however, is still waiting for its Ice Cream Sandwich. Apple doesn't have this problem, and I'd be surprised if uneven OS updates afflicted the incoming wave of Windows 8 tablets. Thanks to The Verge for the tip.