I would say one of the biggest considerations is the height you will be mounting the plasma vs. where you will be sitting. There's a reason most people don't sit in the front row of a theater, and it has little to do with sound. It's because you have to crane your neck back for a couple of hours...
You want to avoid that with your plasma for sure.
I've had many people ask about it with a fireplace, and then we had their mantle lowered, which is often much easier to do than people realize. So, the mantle directs heat away from the fireplace and into the room and is a little lower so the plasma can come down some. The center channel then is placed above the plasma, instead of below it. Works well.
Great details from that link though, didn't know the 90 degree mark was what most plasmas shoot for. I would actually read the plasma owners manual for 'operating conditions' instead of just taking that website at its word. There are likely environmental considerations that will be spelled out for you and some plasmas may deal with heat better than others.
