I remember working for a place that had some big plasma screens for monitoring some things in IT. Unfortunately, they thought that the screens were impervious to burn in. We all saw that management was wrong on that.
According to PC Magazine, has some tips to prevent burn in, but the "break in" period is the most important. Burn-in more likely to happen with a brand-new plasma screen with its "fresh" pixels... Once the plasma has aged a bit, that kind of afterimage is less likely to happen." (Source:
http://www.pcmag.com/article2/0,2817,2330138,00.asp)