Is a screen saver necessary on a flat panel screen to keep it from burning or shadowing like CRTs used to?

Back in the “old days” of CRT monitors you had to use a screen saver to keep information from getting burned/etched onto the monitor’s glass and/or phosphors. With today’s modern flat-panel monitors (LCD and Plasma), can the screen be damaged in the same way? Is a screen saver necessary, or is it just eye-candy?