Venerable Flash animator Chris Georgenes has created a very nice and helpful video tutorial about the new Spring properties that can be set on bones when working with inverse kinematics (IK) armatures in Flash. These properties, Strength and Damping, can be confusing at first, and usually require a little bit of experimentation in order to create the specific effect you are looking for.
Chris’ video helps a lot with this and should save you a lot of time getting up to speed with the new properties.
Chris has also written an article explaining the use of the new properties in detail. The video and article can be found here: