Here is alink from c-net. that talks about this . John
...Certainly, we all know things like playing video games with a lot of their static images can potentially be a threat for burn in, but what about watching a 4:3 picture on a 16:9 screen with the bars on the left and the right of the image. Will these bars be "burned into a plasma display or are the sets designed so this is not a threat. My Sony plasma has grey bars on each side...I'm thinking that this is better than black.