Like the video! Good idea to throw the GoPro in different places to catch different views. It makes for a cooler video.
I love GoPros... my ONLY beef with them is that your always stuck wit a wide angle view. If you had the option of at least a 50mm equivalent (ie. "normal" field of view) it would be awesome. The problem with the wide angle on the GoPro is that you tend to lose the sensation of speed when recording higher speed action like cars. The only way to gain that back is to have the camera mounted very low (within 6" to 10" off the ground) so that the passing asphalt will seem to be moving at speed. The other issue you have with the wide angle is that other cars that might be only 10 feet in front or behnid you look like they are 30 feet away. I always have that issue when recording groups driving through the twisties. Other than that... I love the GoPros. I have two of the current cameras but have owned 6 over the years.
As for the microphone.... it's the only way to go. I have a long cord for the mic and either have it mounted with a suction cup out back to get the exhaust roar or in the car to capture radio chatter (we use two-way radios on road trips) which is always full of crazy banter. One thing that I would suggest there is run a dead cat over the microphone. Basically, a dead cat is a furry cover over the microphone that kills the wind noise. Some microphones have folks that make them. I made my own with some cheap faux fur from the craft shop. The clarity is far better letting the deeper tones of the engine really come through.
