Would love any feedback on our plan below. I know there is another post on this subject but didn't want to hijack that thread.

We are attempting to make sure
--TV is no more than 44 inches above floor level
--installing a fireplace gas insert into our wood burning fireplace
--using "fireplace canopy" that can extend out 6 inches and can be used for "zero tolerance" fireplaces such as gas inserts - eliminates the need for a mantle and thus allows us to keep tv low - e.g. one example of a fireplace canopy here
--plan to use thermometer after installation and look for temperature of less than 105 degrees, if doesn't pass test then will put a more intrusive mantle in place but hoping we won't have to do that
--electronics (tentatively) will be in a cabinet on a wall crosswise from the tv wall with a soffit adjoining so cables can be run (and don't have to reduce height of TV)
(not installing electronics on same wall is most controversial, right now of all our issues - comments?)
--probably will get Samsung 55 inch even though I understand warranty will be voided - live in Texas - not too many nights when fireplace will be used - though more nights than currently used, I'm sure
--side note, plan to use marble tile surround both above, sides and below (if there turns out to be a below) - hearth will be marble slab
We haven't done any of this, still in design stage -- would love any feedback.

There's a lot of variables when mounting over a fireplace: wood, pellet, or in your case, gas - zero clearance insert or real brick built fireplace - then LCD or plasma (plasma generally has cooling fans w/filters that don't like smoke & dust) - smoke is attracted to the screen - temperature rising up to the TV (which usually in most cases is not as bad as you'd think) - height of the TV which should be at eye level at the center of the screen or worse case, bottom of the screen (but then that also depends on how much TV you watch) and yes a tilt mount helps with higher mounts.

Next, is on a finished brick fireplace you don't know where studs are or what's behind them - any installations that I've done I have always gone through the mortar into the stud or header, as opposed to damaging the brick which is difficult to repair if the mount is taken down.

And, the big next, is installing an electrical outlet behind the TV and then finding a way to route the A/V cables to the equipment - running across the brick really doesn't create the "Photoshop look" people see in magazines!

I have done some installations where a remodel was being done and they could open up a wall so you could see inside where you want to mount and figure out a cable route (keep it expandable) and outlet installation.

Having said all that it can be done but I have also have had customers who wanted me to take down an installation somebody else did over their fireplace. I won't do a fireplace installation unless I am very comfortable about the installation, the customer understands everything, and then it will often be much more expensive than mounting on a standard wall.

So, just be sure about what you want and make sure whoever does it, does it all to code... you wouldn't believe some of the stuff I seen such as AC power cords being fed down walls, etc..