I've seen a lot of threads over the years about mounting plasmas above fireplaces, etc.....here is a small tip that may help someone in the construction phase.

Obviously pre-wire above the fireplace (even if you just leave the low voltage in the wall with no box), and have your builder skin above the fireplace with 3/4" plywood.

Sheetrock over the plywood.

you can now hang a gorilla from that wall, with no guesswork....but it also makes hanging art, even odd shapes, easy.

Have you started watching the TV yet? I'm thinking about replacing our 11 year-old floor-standing big screen with a flat panel above the fireplace. I'm worried that it would be too high causing eye fatigue.

I have my 55" Hitachi plasma mounted above a gas fireplace. The mount is angled down towards the viewing area, and there hasn't been any eye fatigue. YMMV