One of the new features in OS X Mountain Lion is the PowerNap energy-saving option that allows newer MacBook Pro and MacBook Air systems to continue to use network and backup services when in sleep mode. However, even after installing the OS X Mountain Lion upgrade, qualified systems may not be able to use the PowerNap feature.
When activated in the system's Energy Saver system preferences, PowerNap will perform hourly checks for new e-mail and updates to Contacts, Calendars, Reminders, Notes, iCloud documents, and Photo Stream. It will also maintain a connection for Apple's Find My Mac service. … Read more