Plasma burn is a problem that got a lot of press when the first plasma TVs first hit the market, but in reality is no longer much of an issue on the newer models. When plasma TV pixels are excited to emit light, they actually get dimmer. The more a plasma screen operates, the dimmer it gets because the phosphors are slowly burning away. Theoretically a static image can “burn” itself into the screen. This was more of a problem for plasma TV owners who were avid gamers than it ever was for people who just like to watch movies in the comfort of their own homes.
If you are concerned about plasma burn, the best way to prevent it is to “break in” the TV by turning down the brightness and contrast for the first 100 hours of operation. Most manuals will give instructions on how to do this and how long it is necessary, if at all. Chances are, if your plasma TV was purchased very recently, it won’t be an issue you have to address at all.