For whatever it's worth, I've had a 58v10 since the first week of November. I'm not exactly certain of the hours of use, but I think it is somewhere around 400 hours or more. After reading this read, I was also concerned that my set had developed or could develop the rising black level problem.
I had my set professionally calibrated a few days ago and the black level measured .0068. Also, I am not certain of the firmware version my tv came with (I believe 1.24, but could be mistaken) but after persistent requests from Vieracast after a few days owning my set, I updated to the most recent firmware which was 1.28. My TV does NOT have the THX problem, and the light output is around 38 ftl without 96 hz engaged.
I feel awful for those affected by various problems, but for those on the fence, there are decent sets out there. I guess my set's black levels could eventually rise, time will only tell.