Apple has released three EFI firmware updates for some of its Mac systems that were released in 2012, which tackle a number of issues pertaining to sleep, Thunderbolt performance, and -- more relevantly to many users -- reliability of Wi-Fi connectivity.
The first update is a Wi-Fi update for all late 2012 Mac systems that improves compatibility with 5GHz-band Wi-Fi signals.
The update includes a new version of the AirPortBrcm4311.kext kernel extension. This update is specific for those running OS X 10.8.2 build 12C2034 (you can look this up by clicking the version number of OS X in the About This Mac dialog box in the Apple menu.
The second update is for 13-inch MacBook Pro models, and it's supposed to improve sleep performance and Thunderbolt router support, and addresses a problem with HDMI display output. This update also includes the 5GHz Wi-Fi band compatibility fix. The last update contains similar fixes, but for iMac systems.
The updates should be available through Apple's Software Update service, but can also be downloaded from the following locations:
As with any firmware updates, be sure to have your system attached to a reliable power supply and follow the onscreen instructions for installing. Do not interrupt the installation, even if it takes a few minutes to restart and install, and be sure to fully back up your system before applying this or any other update to your system.