Apple Enables Power Nap Support for Retina Display MacBook Pro With SMC Update
Apple has released MacBook Pro Retina SMC Update 1.0 to enable Power Nap support for users on Mountain Lion.
About MacBook Pro Retina SMC Update 1.0:
This update fixes several sleep/wake issues to improve the stability of MAcBook Pro with Retina display (Mid 2012) computers and is recommended for all users running OS X v10.7.4. It also enables Power Nap support for users running OS X v10.8 or later.
You can get the update by selecting Software Update from the Apple menu at the top left of your screen.