Today a friend pointed me to a very interesting blog entry about the Belgian Ministry of Education and its use of Apache ServiceMix (by way of the FUSE ESB) to manage over 1.5 million student records and exposing it to nearly 3000 schools. Lilian Duchêne's blog entry does a good job at detailing this system architecture from a high level. Intalio also had a hand in the architecture with it's products as well.
Below is a diagram of the system architecture Lilian describes:
The architecture shown here is fairly common, whereby services are decoupled using JMS messaging via Apache ActiveMQ. Not only does this make the services location independent, but it also guarantees the delivery of messages. Also notice that the services have been kept smaller and reusable and separate from the real back end application. This abstraction is great for scaling the application as Lilian describes in the blog entry.
Another interesting aspect of this architecture to note is the use of VMWare for the virtualization of the entire architecture. I am finding more and more customers seeking virtualization of architectures in this manner recently. IMO, the benefit of being able to move an an entire architecture to another piece of hardware in one fell swoop can't be undervalued.