Thanks to HystericalParoxysm and wes_h for the written examples of this method.
I'm using an example shape, you can do this with any model you have made which has different joint assignments.
I've assigned different weighted vertices to each row.
2: Make sure there are no vertices selected.
Go to the Window menu, and check to Show Keyframer.
Joints tab; scroll to the joint you wish to preview (b_hair is bone 64). Double click the joint in the list window (1).
So it appears in the little window (2).
Model tab; select the Rotate button (1).
Press the Anim button in the Keyframer (2).
Your model will turn dull grey, and the vertices will hide.
Drag the curser in any of the 2D views, and watch what happens in the 3D view.
Notice a gradual curve from the base up to the 3rd row of vertices down, nice and smooth.
I weighted the 2nd row of vertices differently to show how jagged it looks when there is a large difference between weights on either side of the vertices.
Click off the Anim button, and the model will go back to it's original shape before animating.
Repeat steps 4-7 for any other joints you wish to test.