If you ever run your plasma HDTV in 4:3 mode, you should be very aware of this. Most plasmas will display 4:3 mode with two light bars to the left and right of the picture. This can cause burn-in, just like with any other TV. In other words, eventually, if you leave it on 4:3 mode long enough, you will see a “ghost” image of those two light bars on the left and right side(s) when you switch it back to fullscreen mode.
There is an easy way to fix this. I can’t tell you exactly what to do, obviously, since every brand of TV handles menus slightly differently. But it’s rather simple. Set those two “light” bars to dark — in other words, turn them off. And you’ll never have to worry about that ghost image ever showing up.