iPhone3G or 3GS Overheating While Using GPS?

There are some reports popping up that the Apple iPhone3GS  and possibly the iPhone3G are overheating when running GPS-intensive navigation apps. I noticed that my iPhone3G, running OS 3.0, became exceptionally warm after running a GPS turn-by-turn nav app while driving for about 40 minutes. I would not describe the temperature as damaging to the iPhone or to my hand when I picked up the phone, but it got my attention. What are your experiences? Any overheating? Use comments below.