I have a plasma and the only issues I have while gaming are with DARK games.
For those I have to crank brightness, and there's always some static image that gets IR'd on my screen after even 10 minutes of play(granted it'll be present but the severity of the IR won't get horrible until after many hours of play).
Sure it goes away after 1 to 20 minutes of TV, but it's a nuisance and makes me think twice about gaming.
If little things like worrying about getting a scratch on your new car's door panel while in a parking lot bother you, this will definitely bother you.
Perfect example is Forza 2 for the Xbox 360. I've been playing it constantly with minimal TV breaks to cool down my pixels since it came out.
I had a nicely imprinted Laps, placing, and timer boxes/text on the corners of my screen.
Was forced to turn them off in game for a while to continue playing without issues. I refused to put the controller down for TV time
And if someone interrupts you during a game, whether it be a phone call or what not. You have to change the source to a TV signal, or something not static while the game is paused.... or turn it off completely.
Then there's the heat...
But I balanced my priorities like this. I watch far more movies than I play games. Movies on Plasma are superb. Absolutely superb with the window effect and the pop. Gaming is also great looking, but it has its tradeoffs.
These aren't TV's you can just leave on while you run to the supermarket or fall asleep to at night. You'll wake up in the morning with some infomercial screen IR'd into your set.