Today I've passed OCEWCD 6 (1Z0-899) with 96% and I would like to quickly share my experience.
I did it the way everyone is doing it and so can prove it works:
1. Head First Servlets & JSP - read it twice thoroughly and once more to recap in the last week.
2. Servlet 3.0 Spec - I initially wanted to only read the chapters on Async Processing, Annotations & Pluggability, Security, Annotations and Resource Injection. But after that I actually read it whole. It gives you a lot of deep knowledge and was quite enjoyable to read. Furthemore some things like exception handling are only described here. So generally, if you find a question in Enthuwares' tests and not in Head First, you know where to look.
3. API Reference - you can't go without reading all the stuff in javax.servlet, javax.servlet.http, javax.servlet.annotation and doing a lot of coding.
4. Enthuware - i was shocked how similar these tests are to the real exam. Some questions were exactly the same. I was scoring roughly 90% on these to get the confidence.
Generally there was not much surprise on the exam itself after doing all the Enthuware tests.
All in all, it took me one and half months of after work studies with not a lot prior experience in Servlets and zero in JSPs.
Today, I can start preparation for the EJB certification..