Ok heres a few suggestions:
Put the video in any other format than quicktime. No really, any other format will do.
Try to back up more and get the peoples heads in the shots. In some of the clips i couldnt see the persons head who was riding.
Don't over edit the video. Sometimes special effects look pretty cool but when you put too many of them it looks crappy.
Anyway these are just my thoughts, so don't take them too seriously, nice videos otherwise.