Mark asks, "I have seen a number of articles about the size of your viewing surface compared to the room size and how far away you will normally be sitting. What I haven't seen is anything regarding the height that the viewing surface should be. My wife and I have had 'discussions' regarding placement of our television. She has won the battle to keep it in a cabinet behind doors when not in use. But the cabinet is too tall (IMHO). Worse yet, I have her convinced that we should look into buying a flat panel LCD and she want to place it on the wall at the same height that you would place a picture. Fortunately she is somewhat vertically challenged and wouldn't place the picture as high as I would for viewing, but much higher than I would for viewing an LCD from a sitting position on the couch. What would be a reasonable height to place a 42 flat panel?"
If you plan to watch television standing up, placing the LCD screen at the same height you hang pictures is probably perfect. People typically hang pictures so the center of the picture is at eye level (unless they are trying to acheive some unique perspective variation). For normal viewing from the couch, this results in tilting your head back to look up at the screen.
Television screens are optimized for color and brightness to look best when viewing with the center of the screen at eye level. If you typically watch television from your sofa, this means you should position the screen with the center of the screen at eye level. In addition to best viewing conditions for the screen image, not craning your neck to look at the screen has important longterm health benefits. Now this doesn't mean you need to invest in surveyor's equipment to configure your screen exactly at eye level, but using your best guess of eye level compared to the center of the screen will result in better viewing than placing the screen above eye level.