Apple's PowerNap feature in Mountain Lion does have a few requirements and conditions in order to work properly.
SMC update adds the missing PowerNap feature to Apple's Retina MacBook Pro.
While Apple's latest MacBook models support its PowerNap feature, for now it will not be enabled for some.
A bug may cause periodic jittery graphics in conjunction with broken audio in some Mountain Lion systems.
Apple's next OS is due out in July, but when it comes time to upgrade will you be prepared?