See the article at http://www.xml.com/pub/a/2002/02/06/rest.html by PaulPrescod for an eloquent argument on why SOAP RPC violates the RestArchitecturalStyle. A quote from the article says: "SOAP RPC is DCOM for the Internet.".
There's lots of discussion on the W3C TAG mailing list about it. See for example http://lists.w3.org/Archives/Public/www-tag/2002Mar/thread.html -- AndrewJoyner