I've never noticed any IR on my 6-month-old plasma (Pioneer 5080). Before watching anything else, I did run it through 200 hours on the break-in DVD from AVS forum and D-Nice's break-in settings, and I now use his semi-calibrated settings on my TV.
Another huge contributer to IR is
"torch mode", which is often called dynamic. New TVs are set to high brightness and contrast in order to compete in the bright big-box stores with a seemingly endless wall of TVs. Unfortunately many consumers leave it on "torch mode" forever. This doesn't only contribute to plasmas' IR. It also uses more electricity, gives the TV worse black levels, and makes colors inaccurate. Everyone, at the very least, should put their TV on standard or movie mode rather than "torch mode". Be forewarned though. If you've been watching TV in "torch mode" for a while, you're likely to think that the picture isn't as vibrant and doesn't pop like it used too. That's because you're no longer trying to send signals to space with your TV's brightness levels. Try it out for a week, and you'll see that it looks better and more accurate, has better black levels, and is easier on the eyes.