Most of the learning I still have to do in C5 is using Vertex Objects.  I usually use the spline modeler almost exclusively, but I am starting to play with the other modeler.  As I said I have been using various versions of Carrara and RDS for years.  Until recently, I have not had a machine that could handle all of C5s best toys.  I am starting to wish I had started with the vertex modeler a while back.  It gets harder to learn new tricks as you get older :) lol.