Less than a week ago Apple released Mountain Lion 10.8.3 build 12D58 to developers and now OS X 10.8.3 build 12D61 is available for registered Apple developers via Mac OS Center. Developers are asked to focus over AirPlay, AirPort, Game Center, graphics drivers, and Safari.
According to Apple latest OS X 10.8.3 builds includes Wi-Fi enhancements, so testers must have a look on that as well.
Download OS X 10.8.3 Build 12D61