iBO.Net is a more comprehensive, high-level API. It allows you to do things that the web services don't (yet), like create/access/update contacts, events, products, etc; right now the iMIS web services are pretty limited (largely to executing an IQA query and performing login/profile activities). However, iBO for .Net still doesn't allow access to large parts of iMIS (such as any of the .Net modules like Process Management).

There is a third, much more comprehensive API used to access iMIS Business Objects and IQA programmatically; this is the .Net API. As far as I know we don't officially support use of this API, but you can add references to any of the .Net DLLs provided in the iMIS install directory's net\bin folder. Asi.dll, for example, provides most of the base Business Object and IQA functionality, while many of the other DLLs provide specialized BOs (such as Asi.Business.OpportunityManagement) and other functionality.

As far as what ASI uses to write iMIS, we actually use all three (iBO.Net, web services, and the .Net API), although the majority of the code uses the .Net API.

All three APIs will continue to exist in future releases; iBO for .Net will be supported and upgradeable for the foreseeable future. The web services API is due to grow quite a bit (see Don's blog), and as I said, although the .Net API is not currently supported, we do want to make it a supported and upgradeable API in a future release. (It needs some cleaning up and a lot of documentation before that point.)