If we carefully observe the current trend, the objective of all the big vendors is to support 'disaggregation' in the name of composite applications.
On one side, in the name of web 2.0, everything is internet enabled. Your Office applications are available on the Web. You get rich user experience using AJAX kind of technologies. In the name of SaaS, the business applications are also exposed as services over the web. This I call it as 'Webifying everything' in your desktop and Access it on the Internet. Access/Interact & Execute everything on the Web. Internet is the Platform.
OK. This is one side of the story. Other side of the story is, to bridge the structured and unstructured world of the enterprise. The structured business process is always available as web application / Portal on the Internet/Intranet. The unstructured communication always happens over a range of tools including your email client, office applications, workflow, etc. all happening right there in your desktop.
So, Do you see a conflict?. One side - One Team is webifying everying saying 'You dont really need to have anything on your desktop except your browser. Other side - Another Team is saying 'Your desktop is reality. It will not go. And Your Internet app is again a majority. And the best practice is to bridge them both effectively, so that the business process gets executed in entirety without any fragmentation/disconnectivity'. This whole paradigm is now packaged as 'composite applications'.
All the IT solutions will inevitably be torn between these two ends.
And the real solution will emerge only if we meticulously analyze the user requirements and choose the best platform / tools to develop the end solution.
Here is a sample:
Now, the important one - Are composite applications portable across platforms?. The real answer is No. IBM is developing its own set of desktop tools/clients using Eclipse platform. Microsoft is having its own office applications. And SAP is building its own set of composite application using its partnerships between Adobe and Microsoft.
If you develop your composite using any one of the platform, Can your end-user / external user having a different client platform really be able to access the composite application?
The summary is the composite applications do not have the same benefits of SOA, just because it is associated with SOA. They have their own complexities and limitations.