The XML abuse I've seen at work is truly horrifying. We use protobuf for most of our inter-service IPC, but for one particular team one of their customers demands the use of XML so that it can be run through some XSLT "security" filters, so they have to transform a fairly large protobuf object into XML, run it through said filters, and then convert it back to protobuf :( I weep every time I think about it.