Interesting article by David Orchard on the extensibility differences/similarities between distributed objects and web services approaches. Whole article here. A valuable quote from David: "Distributed object systems made a critical decision that any kind of extension required that both sides understand the extended interface. This is the fallacy of "single administrator". Much has been made about the fragility of distributed object systems, and I'm convinced that this lack of "touchless" extensibility was a key contributor to it's lack of uptake and the triumph of the web."

Another useful article from David: Examining Wildcards and compatible evolution