Yeah if your GPS app has like an image on it that never moves or changes, you could get some ghosting. I remember a while ago samsung allegedly promised to replace affected units :thumbup:
My display is burned in through heavy use, no ghosting, just a general fading everywhere except where the statusbar was.
As for heat, get an app that puts temp in the notification panel like Battery Notifier. As a rule, i switch off when it hits 55