Just as a heads-up - SOAP/1.1  changed this to allow any URI in the
SOAPAction header field so this should not be a problem anymore.
As for the specific question that began this thread (whether the
SOAPAction header is useful or not), I can offer an implementation
perspective. We've implemented the 0.9 version of SOAP as a part of
our UPnP implementation. SOAP/0.9 is carried in HTTP and does
include the SOAPAction header. It also includes the same
information (the action identifier) in the XML body of the message.
We found the potential conflict between these to be a major pain
to deal with, especially since the namespace was represented
differently in the header and body (which meant that the comparison
had to be namespace-aware, it couldn't just be the equivalent of