Internally, we have played with Microsoft Office Business Applications for quite sometime now. But, its very exciting to see industry majors like FedEx experimenting with those ideas.
Fedex has recently launched an application called 'QuickShip' which lets you to execute critical functions like shipping&tracking without leaving Microsoft Outlook. It is basically a Microsoft Outlook add-in that talks to FedEx services. I looked at the demo and I should say it was impressive and exhaustive. It has forms and menus built right into your outlook. Above all, FedEx distributes the app for free!.
Its a paradigm shift where companies are moving away from websites to consumer-side apps. And the next logical step would be composite apps that integrates not just FedEx services but with other external/commercial services as well.
Have a look at a list of other experiments that FedEx is engaged with, in Microsoft Sharepoint / Office areas. In one of the offerings, the FedEx data is integrated with Virtual Earth as well.
I firmly believe that we are few steps away from the tipping point for Composite applications.