I'm having this issue too with a 4 year old Samsung PN50A510. I've had a light blue line about an inch from the edge on the right side for years now. That one doesn't really bother me. But yesterday, while watching a movie, a dark purple line appeared much closer to the middle of the screen, and it's far more distracting.
Here's the thing. About a week ago, I had a massive power surge during a storm which took out a PS3, a hard drive, and little light which were all plugged into the same surge protector as the TV. The TV seemed to be unharmed. My insurance covers power surge damage, but I have a $500 deductible, so I haven't put in a claim. However, if this line is a result of the surge, then I definitely should.
So my question is, could this new line have been caused by the power surge?