Apple today seeded build 12D58 of OS X Mountain Lion 10.8.3 to developers, marking the eighth beta iteration of the newest version of Mountain Lion.

From MacRumors:

10.8.3 was first seeded to developers in November. Build 12D58 comes a week after build 12D54, and like the previous build, contains no known issues or features. Build 12D54 brought significant changes to WiFi, and asked developers to focus on testing AirPlay, AirPort, Game Center, Graphics Drivers, and Safari.

 Apple Seeds Build 12D58 of OS X Beta 10.8.3 to Developers