Samsung came through for me too
I had the same darned black lines come up onmy 55" plasma about a year and a half after purchase. After reading this thread, I first called customer service and they said I had to pay for the repair, and then I told them to contact Executive Customer Relations because I had read that this was a well know issue with Samsung TV's. Stretching the truth a bit, maybe....
Before I knew it, they called me back to schedule a service call, and bam! two days later a tech guy came out and fixed the thing (replacing a panel of some sort, or something that somebody referenced on this site).
Now my family is sort of missing the black lines - they say the TV looks smaller now. I don't ask about such things anymore.
Anyway, thanks to those on this site for helping me get this resolved. And let's give Samsung some credit as well, I guess. They did fix it for free after the warranty expired.