I think the important thing to understand is the difference between the exams. Both the SCWCD and the SCBCD are for
J2EE technologies and are multiple choice (like the SCJP). With a good study guide and some practical experience you can gain these fairly quickly.
However the SCJD requires you to develop an actual application from business requirements, using J2SE technologies like Swing, RMI, IO and requires good understanding of Threads, Locking mechanisms, I found that it provides a really good learning experience, but takes a lot more time! You then also have to sit an exam.
I guess it depends on what route you want to take i.e J2SE or J2EE, personally having some web and EJB experience I went for the quick win route, by getting the SCWD and SCBCD multiple choice exams under my belt and then started the SCJD which I have found the most rewarding.
Jason.