I have used a helmet cam quite a bit. I used to make videos at all of the MX tracks in Socal. This was about 5 years ago, but even then the technology was awesome, and cheap, I think I paid about $300 for the set up including a microphone that I wired inside my helmet for commentary.

It worked out great. The key is checking to make sure your camera is level against the horizen when riding, that way you are not looking up at the sky or straight down at the snow.