I use iMovie ’11 (version 9), the ContourROAM helmet camera for video, and my iPhone 4S for pics.
For the fast parts, I tend to use 3X speed, but it depends on how much “shaking” there is. Obviously if you’re going over bumpy terrain, the shaking can get so bad that if you speed the video up it will look worse. It helps to have an object in the foreground so that viewers don’t get disoriented.
You can also experiment with camera placement. In the video you posted, it’s a really cool angle because you get the kid’s perspective. Perhaps if you can affix the camera to other parts of the bike you can get more interesting angles.
All in all, play and experiment. I look forward to seeing your next videos!