As noted by netkas.org and in our forums, the initial beta release of OS X 10.8.3 seeded to developers yesterday contains drivers supporting AMD's latest 7000-series graphics cards, including the high-end "Tahiti" options. The development has naturally sparked speculation that Apple is starting to build in support for graphics cards to be used in the all-new Mac Pro coming in 2013.
This is not the first time that evidence of Tahiti support has shown up in OS X either, as other drivers surfaced nearly a year ago in OS X 10.7.3. Consequently, it is difficult to reach any conclusions regarding Apple's product plans based on the appearance of new drivers in OS X 10.8.3, but it certainly seems to be positive progress toward support of new hardware.
Article Link: OS X 10.8.3 Beta Contains Drivers for AMD Radeon 7000-Series Graphics Cards