Where's HTTPBuilders?
Mark Baker and Steve Loughran write about the reasons for SOAP interop problems. My favorite quote comes from Steve:
The most poignant metric of interop problems is how Sun and Microsoft are so proud of collaborating so that their SOAP stacks will work together. Why don’t you see the same vendors getting together to demo Http client/server or Xml Parser interop? Because if you were that incompetent, people would notice.