I have a plasma 16:9 wide screen TV. I have been told that prolonged watching of 4:3 format programs can burn the black bars into the screen.

How long is considered 'prolonged'? Should I be concerned when watching 16:9 and the commercials come on in 4:3?

NBC's widescreen broadcast does not fill my entire screen, there is a .5" black stripe. Should I be concerned about burn-in with this?

What about letterbox movies (black bands on top & bottom)?

Thanks