in an ideal world I would say no no no ! but sometimes there's just no other place !
it's bad for your neck if it's too high and it's a conversation killer - if you can have it in a pop up cabinet or a standard cabinet with doors that hide it most of the time ?!

If there are no other options...Have you looked into those mirrored frames? They are just a decorative "mirror" when the tv is off :)

http://www.seura.com/

Not unless the room is generously sized.

if the fireplace is a new addition and its gas, then you can adjust the height of the fireplace and you won't have neck problems.

OnePlan is so right -- neck strain, conversation killer, and usually much too big. A pop-up cabinet is a much better option, but another room is the best option. There isn't that much on television that is worth watching so why make it the center of attention.

It seems new homeowners can't wait to place their TV front and centre over the fireplace. Sometimes there is no other sensible place, but as an evening walker, it occurs to me with every single house I pass that I am constantly making (unbidden) judgements about each family's home life as a function of all those flashing TVs I see--and I can see many of them because of course they are so danged high up in the room! Many windows have only their lower half curtained, I think, especially on the 'high' side of the street, in order to have some sort of view over the area. In any case, it is a sort of light and visual pollution that neighbourhoods can do without, I think . . .

No as it seems ergonomically wrong.