For a long time (back in 2006 I was asking for it on CGTalk) I wanted this kind of functionality for Blender. Now, the artist Ivo Grigull is working on a constraint that adds this "spring" motion effect - great for applying the follow through animation principle. Look and start drooling:
It's a Christmas miracle!!! hehehe ;)
And Happy Holidays for you!
Wow, that's very interesting! I just hope that some don't abuse it by using it as a way to avoid learning to animate. It's a great asset, though, if you already know how to do it manually and need a more efficient workflow.