Burn in is due to uneven aging of the screen. CRT's and plasma displays are all susceptible since they use phosphors to show color, and phosphors do age with use.
LCD's don't have anything that ages so they can't get burn in. The worst that can happen with an LCD is the little microscopic rods that form in each cell when its charged can stay that way if left there for a while, resulting in what looks like burn-in. But, this can be fixed by rapidly turning the cell on and off. See this:
Originally Posted by Logical
My old LCD monitor would 'ghost' images that were static for a long period of time. It usually happened when there was very bright white against dark or black. If i switched to full dark or black screen i would be able to see the bright image ever so slightly. It isn't BS and is definately quite common you just dont notice it most of the time.
Actually what you were seeing was the dark parts staying kinda dark, the bright parts were more or less normal on the other hand. I've never heard of LCD image persistence being permanent if somebody takes steps to correct it.