It has the longest name of all Sun Java certificates, and it probably requires you to remember the most little nit-picky facts, but I just got it, and became a Sun Certified Developer for Java Web Services 
.
The exam tests for in depth knowledge about
- XML
- XML Namespaces
- XML Schema
- XPointer
- SOAP 1.1
- WSDL & UDDI
- JAX-RPC. This is the most important part:
- Endpoints
- Handlers
- Configuration
- SOAP and XML Processing
- JAXP
- DOM
- SAX2
- TRaX
- JAXB and SAAJ,
- JAXR
- WS-Security
- you should have an overall knowledge of WS-Security the related standards:
- XML-Encryption
- XML Digital Signature
- XKMS (XKISS, XKRSS),
- SAML
- XACML
- the goals of the Liberty Project
- WS-I Basic Profile (all rules)
- Web service architecture and blueprints
My “How to pass” tips
Get the book J2EE WebServices by Richard Monson-Haefel (RMH) and read it along with Mikalai Zaikin’s (MZ) WSD Notes. Practice a little with building your own web services: download JWSDP1.6 and read Understanding your JAX-RPC SI environment to understand it, and play with the samples. Take some test questions at xyzws.com and see what your co-students think at the Java Ranch SCDJWS forum. Learn a lot, practice a little, and you will pass.
A better tip is to skip the whole JAX-RPC mess and start off using JAX-WS, which is only 2/3 as bad as the former 
!