I love my iMovie. I use it all the time.

I think you could have muted the volume on your video and you can do a stabilizing thingy on it as well. (that's the technical talk). Mostly just play around with it - totally addictive.
I've got a helmet camera that you totally need a dramamine to watch any footage from. I move my head around so much that it's constant motion sickness.
I haven't played with the speeding up thing or slowing down, though I've watched some tutorials on it. A couple weeks ago though, I made a trailer and that was AWESOME. That's in the new version of iMovie.
I love your climbing videos. Makes me want to go out and ride, yet too tired to do so because I feel like I climbed too!