Yes, there are many technical underlying distinctions. All these terms mean different things to different people. Some think of only peer to peer, or of distributed clusters, or even just plain old mainframes with these monikers. Cloud computing is riding up the hype curve right now, so it's going to mean a lot of things to a lot more people. Again look to Wikipedia for excellent background. Nick Carr aslo has a well-received book on the concepts, "The Big Switch."
Even as cloud computing is a moving target as a concept, I think it resonates better with people than "grid" or "utility." People seem to understand compute resources as a service when defined as cloud, and they better associate the services with the Internet. I expect grid and utility as names to fall from favor and to all become lumped into "cloud computing" in the near future.
Therefore, there will be many flavors of cloud computing, with many subsets. Already we have a plethora of "X as a service" (XaaS) offerings, including swapping the X with "software," "infrastructure," "platform," "data," "integration," etc. I expect to see "clouds as a service" (CaaS) any day now. For most enterprises, these can be powerful concepts and methods. We are entering an era where there will be far greater choice on how to acquire, use, test, and generally play around with a variety of hosting and delivery means. Pricing and business models for IT services will also flower and bloom, mostly to the consumer's benefit.
So whatever they call it, take a look at it and see if can begin to work for you.
This was first published in June 2008