Did you enjoy Metin Seven's '3D Equalizer Music Video' yesterday? It must be serendipity that S J Bennett posted a tutorial on how to use F-curves to achieve this effect (the audio part starts at ~ 23 minutes).
S J Bennett writes:
In this tutorial, I go over Blender's "Bake Sound to F-Curves" function and some of its options, demonstrate ways of using the resulting data within objects and armatures, and provide a whirlwind tour of the audio spectrum.
The second half of the tutorial shows you how to identify and extract data from specific frequencies in order to make a drummer armature play the drums using automatically triggered actions - no need to keyframe each individual hit or even open the NLA Editor!
Software you'll need to follow along at home: Blender 2.70, Audacity or any DAW. Leave comments if you want my sweet and juicy source files.