Bones are represented as plain transforms in the hierarchy view as children of the object the animation is on. You'll see the bone's pivot when you selected it's transform in the hierarchy view.
How would you like to "use them"? If you mean modifying the poses/animations, then you should do it in your animation application. If you mean playing animations, then you don't need to access individual bones. If you would like to attach an external object to a bone, so that it follows the animation, you can attach it in the hierarchy view, as described above.
answered Nov 24 '09 at 08:35 AM
Best chance here to get some editor feedback for the placement of your bone is to add a gizmo to your joint transforms: http://unity3d.com/support/documentation/ScriptReference/Gizmos.html
You can even have a 3D shape as a gizmo, for instance a cube, and have a script automatically calculate the gizmo size and orientation by comparing the current joint with the child one(s).
It would probably take some time to tweak it all to perfection, so I'd only do it if you really need to check the "bones" in-editor for some very fine tuning. If you go for it, please consider sharing the script(s) with the community in Unitywiki. Good luck!
answered Jul 23 '10 at 04:17 PM