The current IBN supports 3 methods for application integration WITHOUT our support. We have assisted many customers through our professional services for application integration, custom application embeddeding and other tyupes of integration scenarios.
In our upcoming 4.1 release we will be offering a new Web Services API/programmers guide that will allow any developer to be able to create interfaces between their applications or systems using this API.
In addition we will be providing information on expanding functionality to the IBN platform view our menuing system as well as our web stubs.
For now with the 4.0 version, the customization capabilities relate to custom data/fields via our meta data engine which can render reports as well.
You can also use the existing web stubs definition tool to "point" to your own applications
Finally, you can build direct interfaces to our SQL server data model as well which several of our customers have done to push and pull data from the IBN into their internal or external systems.
Hope this helps...