I pretty much don't use any navigation app unless I can have the phone plugged in to the charger.
Having said that, I use the Navigon App running almost every day on my commute (45 minutes each way), and while the phone is warm when I pull it out of the car charger mount (Pro-Clip), I wouldn't exactly characterize it as hot.
If you want hot, try Waze. It burned down half the battery on my 925 one day in under an hour.