After my SCJP I took the SCWCD exam. It's not very difficult Use the famous Head first book and code some things to practice and you will pass.
The disadvantage of SCWCD is that jsp's and Servlets are not the hot stuff anymore. On the other hand, jsp's and servlets may be assumed to be default knowledge for a developer nowadays. I would like to see SCWCD replaced by (the still non-existing) JavaServerFaces exam. If I remember correctly Oracle had some kind of beta exam for JavaServerFaces . Maybe not many people were enthousiastic.