Just as promised, Apple has released an update bringing PowerNap to the new Retina MacBook Pro. Specifically, Apple has issued a system management controller update, which turns the feature on for the new machines.
You can get your hands on this update several different ways. You can visit the software download page to manually install the update, or via Software Update in the Apple menu for users running Lion, or though Mac App Store updates in Mountain Lion.
I think PowerNap is one of the sleeper hits of OS X Mountain Lion. To me, it’s handing over the mundane task of keeping software up to date, and handing it over to the system to take care of. Granted, it’s not a complete automation of the task, but it certainly is nice to open the lid on your MacBook Air (and Retina MacBook Pro, of course) and find that you haven’t missed a thing.