Sum might not agreed bout the lcd burn in do happen..but..ive seen such cases happen mostly in industrial work where most of the time,the lcd being turn ON all the time (the lcd act as GUI/Monitoring the condition of specific machine)..till the lcd died (either from the dead pixel spreading or the backlight problem occurred).

even for my lcd,im not agreed to let it idling with static image even for 5 min...rather turn the display off..

my 2cent..