Not to be an alarmist, but there may be something wrong with your set. I would keep a look out for other signs of burn-in. I have a Sony LCD, and while the earlier post about LCDs not suffering from burn-in is true, that is only for those that are operating properly. Even on my LCD I had bad burn-in, or more accurately severe image retention, until Sony replaced the entire light engine. It was OK for a year, and then failed in that manner.
Most plasmas dither the signal, or that is, they move it around on the screen a pixel or two every so often, which is supposed to prevent hard edges on burn-in. Is your burn-in definitely hard-edged, or is it somewhat blurry?
If you get a lot of calls, it may be hard to determine if it is true burn-in (which is permanent) or image retention (which should not persist past 24 hours). You might want to turn CID off for a couple days and see if it goes away, and that might narrow down exactly which problem you have. Better yet, freeze on white-on-black credits for a few minutes (no longer) and see if you have retention of that.