I have mounted the display above the place.
I've recently mounted my plasma above a fireplace in my fiance's tonwhouse where I now live. It is a small room, and we were limited to only three spots for the tv, and the other two were just really, really bad from a seating point of view. So above the fireplace it was. I had checked the temps above this fireplace, and it never got above 82 with the gas fired fire going. I also checked at my old place, a wood burning fireplace where I burn oak pretty gosh darn hot, and it never got above 85 above the fireplace. That's the heat issue. The height issue is the second hurdle. My fiance' wanted the tv ever higher, saying I was compromising the mantle and over mantle that I will build shortly from Cherry urban lumber. The center of the tv is currently 5'9" from the floor. The viewing seats are about 10' away. It is a pretty healthy viewing angle. I do have a tilt mount, which helps a bit. We watch maybe three movies a month, and some very, very, light ota tv watching, mostly news. My display is mostly to stream Pandora and for the osd of the music server. We have noticed no neck pain from watching a full length movie. I will say that if I was a heavy tv watcher, or watched three movies a week, it could be a strain. If your seating reclines, or your couch allows you to kick back, it really is not a strain, imho.
Attached you will see the rough in for pulling wires to the display and around the fireplace. I did find some of the wire pulls to be very tough! Electrician's earn their keep and I was cursing a number of times as I struggled to pull the runs of wire through, around, and up into the attic. I am hooked up for whole house audio, zone 2 with a small speaker selector. I am very happy with my display as it is. A classic tough room. Not for the faint of heart as the wiring is a bear. Hth. Pm me if you have any questions about my experience.