I have just passed SCWCD about an hour ago! The main topic I was weak at were web-app deployment and tag-related things, since I had no prior experience with them.
I have prepared from HFSJ book, and I have to say that unfortunately it is not enough if you want to make a perfect score. The title is in fact right, it says passing SCWCD I have also ran through the specs, but considering how "attractive" they are I seemed to not remember much I did not many mock questions, and I also did not really try to code everything, which made an impact on my performance (in the beginning it went away from my mind how to do a simple output from servlet, but I went to further questions to see how they do it there ).
About topics I have to say that there were less questions about custom tag development than I expected and more from web app deployment and security. There were also plenty questions about design patterns, so learn them hard. And not to forget JSP Document model, a.k.a XML-compliant JSP. HFSJ book has only a single page about it, and in the exam I had some 3-4 questions at least related to it.
One of the questions also contained an enhanced for loop, thus making me know that you need to assume JRE 5 for the questions! This helped me because later there was also a question concerning putting long variable into the attribute(or parameter, or header, I forgot now), which means, you can assume that something like setAttribute("long", longVariable_NotLongObject) will work because of autoboxing! I am of course not sure whether I got that question right, but other answers had methods like setNumericAttribute and setLongAttribute, which I cannot find now in API.
This forum also helped me to sort out a lot of things, thank you very much!