I know there is a lot of debate as to whether service design is not just IxD. I don't are (anymore). The reality is that even IxD is an emergent cross-disciplinary field that at earlier points in its history could be totally confused for previously existing design disciplines and engineering practices. But considering the size and breadth of this community with various affinities it is clear as Morpheus said, "We are here." That's sorta how I see Service Design (they need an abbreviation; is SD good enough? for now it will be).
The evolution of interaction design and its many tracks of emergence is not over. What seems clear to me is that IxD has emerged because of the special requirements created towards managing the complexity that technology has caused in people's lives. Without that shift or new reality, IxD would have arguably never coalesced the way it has. (Yes, I know this could be seen as countering my previous arguments that IxD is technologically independent.)
So during my grad seminar last night I was talking about this history of emergence. One could point to industrial design as having emerged b/c of the new realities of the industrial age, but obviously ID has not stopped there. Information Architecture emerged as we know it today b/c of the properties of the "information age" and so on.
So I was thinking about this and it hit me that the emergence of service design has occurred similarly to IxD & b/c it is so similar in emergence, it looks so similar in practice. But what has SD emerged around? Well, like IxD it is really about a new level of complexity. This complexity is not limited to "services" in the exact sense which is why defining what a service is, is not so important, but rather, SD is here to manage the level of complexity that has increased within culture itself. The very means of bringing meaning, of doing economy, of communicating, of leading (doing politicking)--the heart of culture--has gotten so complex that it requires us to re-look at on a fundamental level the ways in which we engage in culture and find new ways to design them.
This shift in managing a new kind of complexity, didn't really require a whole new discipline, but like IxD, did require creation of new tools against the assimilation of appropriate tools, and required the creation of a strong and vibrant community of people thinking about these new problem areas.
One last point, like the industrial and information revolutions, which created deep cultural shifts through society and thus new practices, this new era of cultural complexity was also brought about by changes in technology itself. So the technology is often at the center of the equation, even if it is not being directly dealt with in the solutions that service designers conceive.
I originally wrote this on my blog: http://davemalouf.com/?p=1783 During which I only link to one resource of inspiration that I'll make you hunt for, but I'll just say thank you Peter Morville for running the "Explain IA" competition.