In their reply to Rtings, LG admitted that there is still a variance in their panel manufacturing which can result in increased suceptibility to screen burn.  (This is separate from the calibration look-up table issue).  Anecdotally, it seems that most people are not seeing any problems, but some are, even after just a few weeks.  LG are now including screen burn in their warranty, but only for one year.  Retailers such as JL specifically exclude screen burn from their warranty.