You can burn in a LCD, BUT it takes a very, very, very long time!!!
If were to watch 3x4 image with side bars 24/7 for a couple of months in a row then maybe you might have problem. I doubt that you will be doing this. Burn-in usually is caused by bright stationary image not by a dark image or bars. John
I'd really appreciate your expert opinions on possible burn-in on my new Samsung LN-S2351W. http://www.samsung.com/Products/TV/LCDTV/files/lns2351_final.pdf I find the stretched images to be annoying and am considering putting up with window boxes, and was just wondering if the LAST SENTENCE in this advice from Cnet BELOW still holds true even though it was originally published in 2004 and updated in 2005. My cable installer told me to avoid window boxes 'cause they'll cause burn in on my LCD. Judging by past information and service from my cable provider I've found they usually don't know their butt from third base...
CNET's quick guide to aspect ratio
Both plasma and rear-projection CRT sets are particularly vulnerable to burn-in during the first 100 or so hours of use. During that time, we recommend you watch without vertical letter boxing at all, and that you avoid still images, such as paused games or television shows. After this initial period, the danger of burn-in is greatly reduced. Other easy measures to avoid burn in include: find a set or a source that produces gray bars (instead of black) to either side of the 4:3 image and/or features other ways to combat burn-in; turn contrast down to 50 percent or lower; balance your 4:3 viewing with more wide-screen material; in particular, sports and animation make good candidates for stretching.
Burn-in does not affect LCD, DLP, or LCoS TVs and is much less likely to affect direct-view tube TVs.