Apple's "MacBook Air and MacBook Pro Update 1.0" brings minor tweaks to how the new laptops, announced at WWDC and released in June, handle certain data crunching processes that led to increased power use.
From the release notes:
About MacBook Air and MacBook Pro Update 1.0
This update fixes an issue that can lead to increased CPU power consumption, and it improves compatibility with some USB devices.
This update is recommended for all Mac notebooks introduced since June 2012.
As stated above, Wednesday's update only affects new 2012 MacBooks and is therefore only suitable for those computers.
Apple fails to go into detail regarding what exactly was causing the increased CPU use and USB connectivity problems, but multiple threads on Apple's Support Communities have noted issues regarding port failure and incompatibility with certain external hard drives.
MacBook Air and MacBook Pro Update 1.0 weighs in at 76.64MB and can be downloaded through Apple's Support Downloads Page or via Software Update.