I have a LN52B610 and I have loved the picture. I purchased the TV on May 22, 2009 from one of the REALLY big box stores.
My wife likes to leave the TV on all day whether or not she is actually watching it. Lately after it has been on a couple of hours the picture begins to go from pure black to normal picture.
On a couple of occasions the picture has gone completely black and the TV has to be turned back on in order for there to be a picture. I do not recall seeing the steady red LED that would indicate the TV turned off.
It seems to be happening more and more often.