Same problem here. Under 10.8.1, I could plug in the HDMI cable and it would display on my TV. A few days ago, I upgraded to 10.8.2, and now my screen goes black on the Retina MacBook Pro when I plug in the HDMI cable if it's connected to the TV. It seems to transmit that black screen to the TV. The reason I say so is that I can see a magnified white outline of my cursor against the black background on both the laptop and on the TV. I get the sound, and I can move the cursor around on the TV screen. (You might not see it because the cursor can fall off the edges---the black desktop is bigger than the portion you see on the monitor), but everything else on both screens is black.
Also, after the upgrade, I started getting weird graphics artifacts in Safari. The red-yellow-green buttons in the upper left get underlined---short horizontal red lines under the red button, yellow under the yellow, etc., and gray lines under the window title text.
I think Apple is struggling with the video system on the rMBP. Under the version of Lion it came with, I got multiple crashes per day. An upgrade to 10.8.1 fixed that problem completely. It worked great on the laptop and the TV with no crashes. Now with 10.8.2, I can no longer connect it to an external monitor via HDMI, it appears. I wonder what surprises 10.8.3 will bring.