I'm no professional when it comes to POV camera mounts, but there's got to be a good reason Vimeo member Enrique Rodriguez added counterweights to the rear of this helmet cam for DSLRs. The video is not in English, but i'm sure you can all figure it out. Looks heavy on the head, but it does serve for some pretty useful POV shots. You can find more details over at the Vimeo link. [Thanks Enrique]
Yeah I know, looks totally dangerous with the weights, but helmet mounts have been done before. Here's that stillmotion video from the NFL.