I have been using my late 2011 Macbook Air with OS X Lion to view movies on my LCD TV. With an adapter, I plug an HDMI cable into the Thunderbolt port and run that to the TV. The Air automatically detects the external display, and I have it set to use that as the main display when it is connected. WHen I disconnect the TV the main display automatically returns to 11" Air screen. It has worked quite well.
Today I hooked up the TV, the Air 11" display turned blue, as it normally does when the TV is detected and the main display is changing over to the TV, but then the display came back on the 11" screen. When I unplugged the TV it did the reverse, turning blue like it was resetting the display again, but the whole time it never goes to the TV. And the TV does not show up under "Displays" when plugged in, even if I run "Detect Displays".