you also have to pay attention to what you are doing and the make
pioneer, panny, and samsung are going to be your best bets against any IR in plasma's with Panny and Pioneer probably ranking significantly higher than the others
most have stuff to try to help if you acquire significant IR, secondly you have to know what you are doing, the first 100 hours or so (give or take) is when the plasma is most susceptible to IR
so going through the motions, if your father bought a cheap (especially the older the model the more IR problems it can have due to technology leaps) plasma, ignored the warnings, had the image settings through the roof, and did what he did long term, its likely some sort of image issues would happen
IR exists, but more or less now of days a smart user can never really see it
case point, i have last year's panny model (42-P700u), for the first 100-200 hours i had picture settings low, no real long static images during that time....not to long after breaking the barrier of the "break-in" period, i played super paper mario on the wii for 5 hours straight one night with pretty much no IR period even when I finally shut it off, i play my PS3 all the time, etc, i have no problems...if I even remotely think I see IR i just throw it to something with a lot of bright colors with a moving picture and it fixes it
to each his own