When I was getting ready to buy, I went to several friend's houses and looked at how high they had their LCD and Plasma screens mounted, and I actually only saw one that I thought was correct, it was centered at eye height with your head in it's normal position while sitting. No looking up, no angling the display, etc. I did mine exactly the same way, and it's great. I would guess the bottom of the TV is about 26-28" above the floor.
One of my friend's has it over the fireplace, and it makes a great picture frame when showing jpegs, but it's way too high, even in a recliner, with the screen angled, it makes my neck cramp up.