It's important to understand that service oriented architecture, when practiced successfully, is not just a technology architecture. The SOA paradigm is really about modeling the business processes, which are not always supported directly by technology components. Ultimately, services may be implemented by technology components, but the business processes themselves are more important than the services that support them.
SOA as a technology is an enabler. The technology doesn't provide direct value. It's not necessarily less expensive to develop services on a line-of-code basis as compared to EJBs or .NET components. Instead, SOA technology should be seen as an enabler of other benefits, such as improved and broader reuse, better responsiveness to changing business processes, and better alignment with business processes.
Dos fuentes contínuas de conocimiento sobre SOA y Web Services son los grupos de discusión de Yahoo: Service Oriented Architecture, de Gervas Douglas, y Web Services Latinos, de José Carlos Del Arco. Hace tiempo que les debo mencionarlos.