OK, so the built-in mic on GoPro is crap. I think it was only designed to supress the wind during crazy extreme-sports stunts. Subsequently, it supresses all audio 
Luckily, starting with GoPro Hero HD 2, there's an external audio jack.
I have just improved my GoPro audio - so much that you won't believe the difference! - using tips from here: http://walkingad.com/#goproherohd
Didn't cost me anything since I just reused some parts lying around. HIGHLY recommended! Now i can actually get very decent audio on my GoPro, which helps all around.
Luckily, starting with GoPro Hero HD 2, there's an external audio jack.
I have just improved my GoPro audio - so much that you won't believe the difference! - using tips from here: http://walkingad.com/#goproherohd
Didn't cost me anything since I just reused some parts lying around. HIGHLY recommended! Now i can actually get very decent audio on my GoPro, which helps all around.