Although it is fair to say that SOAP is slow, it's getting better and one of the more interesting advances came with the development of the SOAP Message Transmission Optimization Mechanism (MTOM) specification. MTOM has quickly become an important component within the Web Services developers arsenal, offering the composability of base64 with the transport efficiency of SOAP with attachments. But unfortunately it wasn't tied into the rest of the Web Services architecture: there was no standard way for services to advertise that they were "MTOM ready". Until today that is.
IBM and Microsoft have recently submitted WS-MTOMPolicy to W3C. This has now been acknowledged by W3C, which opens the way for a standardization effort around this.
