I had slight burn-in on my Plasma after the 1st year because I never stretched the 4:3 material. One day when I was watching a scene where there was a clear blue sky on the entire screen, I noticed that the side pillars were "brighter". I freaked and started to stretch from that day on. Since it was slight, the rest of the screen appears to have caught up, and I can't detect the pillars anymore.
I have just noticed this exact thing on my cheapo 26" Polaroid LCD. Although since I stretched it from the second I noticed it ( and I hate it stretched but oh well) it has gotten better. Hardly noticeable on HD stuff, but when I watch stretched soccer matches on fox soccer channel, you can see it much more on that green field.
I also thought there was no fear of this on LCDs....and although it might not be permanent....I'm very disappointed.