One camera on the stern on one of the US boats today. We experimented with a "low cost" wireless microphone that I patched into a GoPro HD camera. The results were "low". Good video, poor sound. I have had great success with the Sennheiser wireless mics with the GoPro HD, (used in College Nationals) but they are more expensive, the lesson here, is you get what you pay for.
Here is a sample video...can you say tacking!?