Yup, if that's the type of stuff (spontanious) you're looking to capture, you're gonna need a helmet cam with some sort of storage device that will allow you to run the camera the entire ride. I've mounted a digital camera to the top of my bars, and have had some success with pix and vids. Certainly nothing exciting, but here are a few examples: (fyi, Windows Media format)
Also, you may want to turn down the sound a bit as wind noise is a bit of a problem.
Urban Ride 3MB
Road Ride 9MB
... Brad
Love the finish of the 'road ride'. Made me laugh out loud. Keep sharing 'em. Thanks!