I've done alot of helmet cam stuff with mini DV. The quality is pretty good, not DV of course, but it does offer some unique ways to mount a camera.
Sadly I have not been sailing much in the last few years so I don't have any sailing video using a helmet cam to show, but I have done some with white water rafting and sea kayaking.
Might check out:
http://www.helmetcamreview.com
Another alternative for excellent quality is a Sony waterproof case for their mini cams. Don't know if they have them yet for HD cams or not, but I get great quality from my little mini DV tape cam in their housing.
Here is a little clip using the WP housing and then some rudder cam:
http://media.putfile.com/Wind-and-Waves ... helmet-cam
Here is the vidicam in the WP housing:
http://media.putfile.com/Baja-whale-shark
Here is me and my entire (waterproof) helmet cam system getting a dunk:
http://media.putfile.com/Man-overboard- ... helmet-cam
Cheers,
Brian