Hi Stan - Is your set 720p? 1080p? What is your viewing distance?
Here are a couple of excellent sites for calculating ideal size (also keep in mind that TV sets are not typically measured by height, they are measured by diagonal in inches).
The ideal "height" of a TV should be eye level when you are seated. This will not only provide the best picture, but reduce neck strain. (The same issue as sitting in the front row in a movie theatre.)
That is one of two reasons why mounting a TV above a fireplace (as often shown in ads) is strange. (The second reason is the heat from the fireplace is a bad thing.)
The set that I will be getting in the coming weeks will be 1080p. The current viewing distance is around 14-ft. I will take a look at the links. Thanks!
Slight correction: The "ideal" position is actually where your eyes are 1/3 of the way up the screen. This is due to the fact that most people don't sit with a straight back when watching movies or TV. Almost everyone is slightly reclined and having your eyes at the 1/3 mark allows them to naturally look at the center of the screen due to the angle of your upper body.
Of course, this is somewhat dependent upon your screen size and seating distance, so most people just shoot for the 1/2 way point.
I would say 1/3 of the way up is more important if you have two rows of seating, with the back row on a riser (not uncommon in front-projection home theaters). It's a good way of ensuring the back row won't have to crane their necks down, but the front row can still view comfortably without craning up. In my own theater, I have but a single row, and I aimed for "about halfway" -- it's worked out well.