Confirmed working, AMD Radeon HD 7970 GHz Edition on OS X 10.8.3, Mid 2012 Mac Pro, no flashing required. Also confirmed working since 10.8.1 beta. Strongly believe this is here to stay. Beautiful hardware. Real-time playback of full-resolution 4K footage in FCPX. Also tested with Adobe apps and lots of GPU crunching. Stable. No issues at all.