Steve Loughran:

The best part of SOAP has to be the orthogonal header mechanism. The worst part has to be how today’s stacks try and map the message to and from native classes, hiding the message from the caller.

+1.

(Just for the record, though: I do actually disagree with Steve’s assertion that you don’t need WS-Security (or something conceptually similar) with REST, and can just replace it with HTTPS. And I also believe there is nothing worse than XML-RPC.)