Optrix has made that process a little simpler by creating the Optrix HD, a rugged water-proof case for the iPhone and iPod touch that can be mounted on your helmet, bike, or anything else to shoot video while you're literally on the move.
Optrix claims the case is "tough enough for military use," so it can handle any falls or tumbles it might be involved in while you're wearing it. The case also comes with several mounts made of "military grade materials utilizing ultrasonic welds and silicon gaskets designed to keep moisture and dirt at bay."
There are certainly quite a few sports cams out there that do the same thing - and with dedicated form-factors and attributes like wide-fields of view, you would expect better results in many cases - but the upswing of the Optrix HD is that you can take advantage of the 1080p video recording capabilities of your iPhone without having to purchase a whole new rig.
The Optrix HD costs $79.99.