Helmet cam videos can be great, but they are tough to pull off successfully. Usually, the camera is bounced all around so that it makes the viewer dizzy. Or the camera is aimed too low and you only see the front tire instead of the trail ahead.
IMHO, helmet cam video works best when spliced in with other trailside video. Also, good image stabilization is a must. And it works best when there is a rider ahead of the camera to focus on. Just my $.02
never ever mount it next to your wheel and make one of those videos in which half the screen is consumed by a tire and spokes.
Helmet cam is dead. Cable cam is what's next. Check this from the guy who runs bikerag.com:
http://myspacetv.com/index.cfm?fuseaction=vids.individual&videoid=31146371
I have a vio sport helmet camera. I've been really happy with it and they have great customer service. In the past I posted up videos from six mile, Ringwood and allaire on the site. They came out decently well, but as dhsean said can get a little bit boring. The video editing is a pain in the @$$ too since you end up compressing a 2 hr ride into a 3 min video. Before you know it you've killed 5 hrs putting the video together. I didn't bike with the camera at all last year, but I can bust it out some this year if people want.