With mounting Flat Panel screens on the wall becoming far more numerous now it will not be long before we start getting health warning reports of repetitive neck strain due to people mounting these things too high on the wall.
The correct height when mounting any screen is; centre of screen at or near to your line of sight, just the same as speaker positioning is best at ear level. The shorter the viewing distance the lower the screen should be if you have to look up this is not a comfortable viewing angel. (Lots of people mount screens more for the aesthetics than for comfortable viewing)
If you like sitting on the front row of the cinema? Stick your screen up hight.