Rich Zygler has a few choice words concerning the implementation of WS-* web services in PHP and how they compare to other methods (like SOAP and REST).
I'd love to give ws02 a fair shake because they have an open source business model. They have a web services framework for PHP which seems interesting from an academic standpoint. But I think WS-* web services are WAY too complicated when compared to REST.
He points at a certain bit of documentation (to show the "simplicity" of it) and gives a personal example of his SOAP experience with the Amazon API as well as mentioning other opinions on the matter.