Apple is seeding a new beta of OS X 10.8.3 to developers, says AppleInsider. The build is labeled 12D54, following up on the 12D50 release posted on January 8th. Any important changes have yet to be discovered, but it should continue a trend of having no known issues while cleaning up any bugs in previous code.
In earlier v10.8.3 releases developers have been asked to test AirPlay, AirPort, Game Center, graphics drivers, and Safari. The betas have also included the OS X Software Update Seed Configuration Utility, which can pull down new distributions via Software Update. It's uncertain when the finished version of the update might be launched, but Apple rarely seeds more betas than it has for v10.8.3.