Surfacing recently is the experimental/android-3.8 repository. This experimental kernel is derived from the Linux 3.8 source tree plus Google engineers layering their modifications atop to make it suitable for Android's use. The work is labelled as "experimental" but it seems to be evolving fast.
It's not clear what their plans are for the Linux 3.8 kernel roll-out as they also are still maintaining 3.0, 3.3, and 3.4 versions of the Linux kernel. With "Jelly Bean" they are presently shipping the Linux 3.0 kernel.
In the coming months it's expected that Google will release Android 5.0 "Key Lime Pie", which is where the Linux 3.8 kernel on Android could make its debut, though that would be a fairly fast turnaround time for pushing it onto Android devices. Regardless, Google developers are now working on an Android 3.8 kernel and the source is available for those interested.
Fortunately, with more Android components being mainlined in the Linux kernel, Android's source tree is becoming much closer to resembling the vanilla Linux kernel. With the Linux 3.9 kernel is where Google is now mainling Android's Goldfish. The features of the Linux 3.8 kernel are talked about here.