Above are some pictures of the Gopro mount I bought a few weeks ago. It is very simple mount and doesn't take up much room on the deck or effect the stability of the kayak to much. The mount is available on Ebay and other sites like Deal Extreme for about $20 - search "Gopro extension". The suction mount comes separate.
I have only used it on sea kayaks (plastic) and it has worked really well. You do have to find a smooth surface for the suction cup to stick but this isn't and issue on composite kayaks. I don't think that it will be ridged enough for white water as the impacts are very hard compared to sea kayaking. Make sure to tether the camera to the deck lines just in case it comes off!
Here is the mount in action. Enjoy
David Horkan from Paddle & Pedal. Posting info on various outdoor adventures in Mayo and around Ireland.