I am often asked what is the difference between these architectures or whether Cloud Computing is replacing SOA (Service Oriented Architecture).
Let's remind ourselves:
Cloud Computing is a deployment architecture that abstracts what we want to do from where it gets done. In addition a cloud is a pool of virtualised resources that ideally offers exceptional scalability.
Service Oriented Architecture is an architectural style at the application architecture or even enterprise architecture level. SOA is fundamentally about building services that when composed deliver a rich application or business process.
These two worlds can and will intersect ... when a service is deployed in a cloud it becomes a cloud service.