One big question about SOAP is performance. Other is transactional semantics. SOAP Performance is a question TechMetrix will address in the coming months. We are waiting to have stable and fully featured SOAP implementations in order to conduct performance benchmarking. The design goals of SOAP clearly don't address Transactional Semantics.
SOAP simply defines how to call a remote method and get the result.
That might not meet all application requirements, but it'll certainly be used by a lot of people. It shows that interop can be achieved when WSDL is available. Send a letter .