I think the only time the TV should be above the fireplace is in a room that you do a lot of entertaining, but don't spend much time in otherwise. Having it there is great for a Super Bowl party where people are sort of milling around, eating, talking about the commercials.
I had a bit of an epiphany a few years back when I thought about how often my mom told me not to sit so close to the TV when I was a kid. All these years I assumed she was worried it would ruin my eyes. Then I thought about how we sit a few feet away from our computer screen, sometimes for hours.
So I asked her about it and she said, "It's because we couldn't see the TV through your head."