Power Nap arrived for the MAcBook Air Mid 2011 and 2012 a couple of days ago. Now its the turn of the Retina MacBook Pro. Power Nap allows your Mac to perform many functions while in sleep mode.
All you need to do to make Power Nap work is to have one of the three Mac models (Air Mid 2011, Mid 2012 and MacBook Pro Retina Mid 2012), have Mountain Lion installed and download an SMC firmware. You can grab de MacBook Pro Retina by clicking on this link.