Depending on how old your Plasma TV is, anything left on there will burn in. As long as everything keeps moving, and there is nothing in one spot for an extended period of time, it should be ok.
It will burn just as a movie and a newsticker does. That is if you leave it on for 24 hours withouth moving anything. Yes it will burn then.
But if you play normally it won´t burn anything. So if you leave the Wii on, when you go eating, just make sure you shut off the TV.
Plasma has a 30.000 hours life (8 hours a day= 9 years). After that you will see the image getting worse. LCD has 60.000 hours....
