One of my customers has a requirement to use United Parcel Service to ship large and small packages. UPS has a great set of documentation, but they handle large and small packages with different technologies. Small packages are simple XML request/response transactions that provide methods for requesting a shipment, accepting shipments, and voiding shipments. Large packages allow you to request a shipment, but the request/response is all in SOAP, something of an overkill in my opinion.
UPS requires lots of data concerning who, what and where to establish their pricing. Data is sent to a URL/end point and a response is returned. The response includes pricing and tracking numbers, as well as image data for printing barcoded shipping labels. So, it is mainly a data transfer operation-- a single service.
SOAP is great if you have lots of defined services, like weather in Seattle or Paris or zip code 94705. Or conversion of units from/to. But for simple data transfer, REST, or just plain old XML request/response is much more efficient.
Here is a diagram of the complete data transfer...
As you can see, there are lots of communications. The first question is, why is there a server in the middle? Well, here's the deal--the SunReturns client is just that, a client. The data really resides at the DataServer--the client simply persists it's own private session. The UPS server is at their site. All communications are via SOA/services--some simple request/response (ala REST) and others use SOAP.
The technology used in the middle is grails/groovy. The SunReturns server is currently a mixture of JSP (legacy) and groovy/GSP. The groovy components are XML only and include controllers, services, domain objects, etc--similar to grails but without the Hibernate layer. It talks to legacy databases, both Oracle and MySQL--not impossible with grails, but definitely outside the conventions.
Conclusions: The natural loose coupling of SOA provides a new vehicle to solve business problems. At the same time, distributing business processes across diverse servers provides a workable migration path to newer technologies. Groovy, grails, and simple XML transport provide a way to implement SOA with a minimum of effort.