I finally got round to trying my new camera mentioned above:
http://www.myactioncamera.co.uk/shop/cameras/ac32-sport-plus/
It cost £80 at the Cycle show. It's a bit more than a camera because it has a GPS too and records the GPS data with the film, so it can do some interesting things. The manual is too complicated for me. It shows how to do work-outs and calories and stuff like that. I got this far, which is probably enough for most people: The blue line is elevation and the yellow is speed. The others are X, Y and Z acceleration, which might be useful to find out how much 20g hurts when you crash or what the terminal velocity of your bike is when you ride off a cliff.
The quality seems pretty good right across the frame. I stopped the playback and took this screenshot:
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It's waterprrof to 3 meters and has a 3 hour battery recording time. It comes with a handlebar mount , USB lead, 8gb memory card and USB card adapter. Not bad for £80. Now £160 on their website. Maybe you can haggle.