The SpyderCam is an invention of Earl Wiggins, a former stuntman. Think of it as a cable car with a camera mount.
Earl's rig is a huge improvement over previous camera systems. His rig can move cameras at speeds up to 60 mph. It is computer controlled, and is accurate enough to stop within two inches of an assigned point. The platform can support anything from a Bolex to an IMAX camera with a full magazine.
The SpyderCam system uses high strength polymer ropes attached to winches. The system requires a mere two points to rig. The rigging towers can be as far as 2500 feet apart. The winches at each attachment point control lateral movement. The two winches move in sync so that a T shaped metal piece moves between them. Extending down from the T is more polymer ropes with a camera platform at the end. This has a winch on it that enables vertical movement. The platform can also be moved vertically and rotate, giving the appearance of three dimensional camera movement. If full 3D movement is required, often, the riggers can manage by moving one of the attachment points during the shot.
I will try my hand at ASCII art to show what I am talking about:
This interesting piece of hardware has been used in many films. Minority Report, A.I., Stuart Little II, Cliffhanger, Batman movies, Spider-man, A Time to Kill and many others have used the SpyderCam system. The one issue, similar to that of Panavision cameras, is that you rent the system, including the crew, you don't buy it. This means there are almost no problems, but it costs more.
This was done for the e2film group. I used www.spydercam.com and the June 2002 issue of American Cinematographer as sources.