I have a MBP 2011 running OS X Lion. I just got a mini-display to HDMI cable so that I can hook it up to my HD LCD TV. When I hooked it up the picture was grainy and the colour was wierd. I tried to change the resolution and went through all the options that my mac gave me, but nothing made the picture better... There was audio though...
When I hook my wifes PC up useing the same HDMI cable and input, the picture quality is HD.
MacBook Pro (13-inch Late 2011), Mac OS X (10.7.4)