I tried mounting my Sony MiniDV cam to the bike, but the vibration upset the tape transport so there was lots of hash in the video.
I wound up getting a so-called helmet cam from these guys
http://www.helmetcamera.com/
and mounted their little remote cam to the bike with the velcro strips they supplied. Their remote cam plugs into my Sony DV and it works like a charm. I put the DV into a padded bag on the rear seat.
One problem is that wind noise will kill the mic audio recording. I put some foam over the mike and mounted it at the rear of the seat to pick up the exhaust note. That worked fine.