Older plasmas suffer from extremely fast burn in, whilst newer ones only suffer from pretty quick burn in. On newer screens, the screen burn can usually be reversed by leaving it on a high-contrast cyclic display, like snow from a static channel.
At any rate LCDs don't suffer from burn in at all.
My laptop has a Clearbrite screen (and it really does look nicer; without that anti-glare finish there is more accurate and vibrant color.), but I was more talking about plasma and LCD televisions. They wouldn't use a plastic cover over any TV, because warping would cause distortion in the picture and reflection, and as far as I know, they haven't made any LCDs with glass panels.