Mind your interfaces!
Haralampos Routis writes wise words over at the Spring Web Services forum:
In my experience, when you have to build a system that interoperates with others, you must pay attention to the interface that you provide. The implementation of the interface is important but it also can change in time. The interface on the other hand cannot/should not change.
So, if you allow me to give you an advice: Use whatever product, framework, soap stack best suits you, but invest on XML Schema and WSDL, because these are the essence of Web services.
I couldn’t agree more!