Oh the overheating/reboot issue is brutal. Since the 2.2 update, the navigation app does a restart - not a full restart through the eye animation - but it does crash and restart in some way with the htc screen (at least for me). Last week, in near 100 degree heat in LA, navigation app overheated phone and went into a never ending restart loop. very frustrating especially when you're using the navigation app... since you need it to know where you're going in an unfamiliar area.
Google Nexus 4