As I've been pointing out, SOA and cloud computing are linked concepts. The fact of the matter is that you need to leverage a good SOA approach to create a healthy architecture leveraging cloud computing providers. Here are a few advantages of leveraging SOA along with cloud computing:
First, the ability to move services around as required by the architecture in support of the business. For example, moving customer transaction processing from an on premise application server to an application server running within a cloud-based platform, such as infrastructure-as-a-service or platform-as-a-service. Since you're dealing with the applications at the services level, they are location and platform independent and it should matter not where they are hosted.
Second, the ability to leverage virtualization, or addressing core applications as logical instances that may run on any number of physical server instances, providing better resource utilization, and scalability. In essence, you are talking to the applications through the services interface, and the location where the instance is actually running is transparent to you.
Finally, the ability to mix and match services for use within composite applications, such as mashups, or processes. This provides the agility aspect of the use of cloud computing architecture and SOA. You're not only able to create applications processes quickly to solve business problems, but re-create them as needed, thus providing the core value of agility. The use of cloud computing provides even more value since we're doing this using more cost-effective computing platforms.
I suspect that more links to SOA from cloud computing will spell success for this hype-crazed concept that is creating a bandwagon that most are jumping on. But at the end of the day, it's JAA, or Just Architecture Again. Perhaps with some new toys to play with, but we love toys.