This video tutorial, via MacMost, takes a look at making a music video in iMovie 2011 using Beat Markers.

Beat Markers allow you to set points in an audio track and then drop in video with cuts that match the beats.

After timing out the beats in a soundtrack, all you need to do is drag and drop video or photos into iMovie and the video will be cut to match the markers. You can also add transitions that fit along with the beats.

via Oliver Chesler