We've(work) got a sony Plasma (not sure what gen,but 3yrs old), it has screen burn CNN in the bottom right hand corner. What kinda money should I be asking for this. Ballpark, I don't want it, but it's an asset that i have to sell.
Once that CNN logo has been 'ghosted' onto the display it will be all but impossible to remove it - if you do see a 'ghost' and it stays visible after a few minutes get your displays 'screen saver' mode into action straight away; and its not a matter of minutes but possibly an hour or so for some displays.
Running your display in its screen saver modes - or even as you suggested an all white slide - for a long period wont cause it any harm; when creating content for digital signage solutions we often include 20 -30 minutes of all white at the start of each 'programme' and the programmes are usually auto started each day using a Crestron or similar system and this along with pre programming the displays to run there internal screen savers at regular intervals ensures we minimise the possibility of screen burn on commercial installations.