I have just bought a new MacBook Pro (OS X 10.8) and try to connect it to the HDMI port on my Sony Bravia KDL-40EX710. I get a clear picture of the computer screen on the TV, but every 1-30 seconds the TV screen becomes black for about 1 second. I tried the same thing on another Sony Bravia TV with the same result. When I tried it on a Samsung TV everything worked fine without interruptions.
It appears this has only happened since the introduction of Mountain Lion as it wasn't an issue with Lion, so I'd imagine it will be fixed with future Apple updates as Mountian Lion is still pretty new..