Why use Digital Video Motion Analysis in teaching physics?

Digital Video Motion Analysis can be considered an invaluable tool in most physics classes as a learning and teaching tool. What makes it worthwhile?

Extends the length scale over which motion can be analyzed: Our motion sensors work well for measuring motion over a narrow distance range (0.6 m -- 2.1 m). Using video, the range greatly extended (inside: 0-4 m, outside 0-30 m; both with 0.5% resolution).
Measures in two-dimensions instead of one: The motion sensors seem pretty useless for other than one measurement at time. Video tracks motion with little distortion in the plane perpendicular to the camera direction.
Taken together, video makes it possible to analyze a great variety of real-life motion, outside of a lab: This is the biggest point: In the AP Physics course it was the decisive point: I most wanted to bring real examples of motion into the class and then try to understand them; I wanted my students to go out and find their own examples of types of motion in sports and work at understanding them.

What makes it challenging?

Analysis Software: Now a non-issue since there are a number of programs now available; I chose VideoPoint (by Lenox Softwork with Dickinson College professor Priscilla Laws and collaborators), which works on MacOS and Windows and has a reasonable licensing agreement.
Video to analyze: Grab a video camera and videotape your experiments (well, it's not quite that easy, but usually you get some good shots on Take 25).
Getting it in digital form: This required specialized hardware and software until recently that usually never quite worked the way it was supposed to. When I was looking (June 1998), Apple had just come out with a version of their PowerMacG3 with integrated video digitizing hardware and software that made it possible, and now with the G4 and iMovie a real-time video experience.
Student involvelment: I've made it a component of a required group project that was to be presented to the class. Students organized themselves into groups of 5-8 students to work on a topic of shared interest; each group contained a few people who could manage the technical side (and recall that this was an AP Physics course).