Well, here is a thought of mine. I have the Otterbox defender case and nutshell iPhone OtterBox Defender Belt Case. I modified the Otterbox defender clip to be a car mount. I am thinking about getting a second clip for mounting on my motorcycle. Maybe mounting it on the bars or something?
I had the 2G and just keep it in my pocket and ran the ear phone cables under my shirt. Now that I have the 3GS I wouldn't mind seeing the screen for the map. Plus, now that we have stereo bluetooth probably going to go to a bluetooth headset so no more cables.