This aired back on March 25, 2009. The link below will take you to a 7-minute segment from MLB Tonight which airs on MLB Network. In this clip, Harold Reynolds is joined by Dr. Mike Marshall and his left-handed student Joe Williams.
With only 7 minutes in which to work, Dr. Marshall has to skim over a lot of things, but he sums up his arm action very succinctly. He briefly explains the muscles that are involved in his arm action and mentions how pronation helps protect the elbow.
Dr. Marshall also has Joe demonstrate a couple of drills. Pay special attention to the second base pick-off drill. It's a drill he has mentioned in the past when talking about re-training traditional pitchers to correct the flaw of horizontal shoulder flexion.
With the football drill, Dr. Marshall and Joe show Harold how to throw a pronated curveball. The video isn't the best, but if you look closely and use some imagination, you can see the ball spinning forward instead of backward.
MLB Network: Dr. Marshall talks pitching
[Update 2019: Link no longer works after MLB.com made changes to their video library.]
Post questions and comments here, and I will do my best to address them.