Daniel Martinez Lara gives a great demonstration of how to sculpt shape keys in:
In Blender 2.58 you don´t need the Anisculpt scripts anymore, just create a shape key and sculpt it :)
Sculpt,Sculpt,Sculpt, I love sculpt stuff, is one of the most direct way to create. You don´t need to know technical stuff, just a bunch of brushes and your own art. It would be nice that in near the future you can pose your bones of your rigged characters with this kind of tools.