Looking up the definition of the Business Data Catalog gives me:
Business Data Catalog: A shared service that stores information about the data in business applications that exist outside Microsoft Office SharePoint Server. You can use the service to display business data on a SharePoint site.
Ok. Sounds easy enough. Now try to engineer a solution for your customers; giving them guidelines on what type of performance they can expect, under what conditions will it require them to buy more hardware, the credentials necessary to obtain the data they need, etc and you get something that isn’t so easy any more.
My PM wrote up a one page specification and we will go through a larger, richer, more comprehensive spec in the next few weeks. The biggest, glaring issue, is the latency factor. There are so many nuances that can affect it and trying to replicate it for the purposes of testing and developing a guideline will require much MUCH thought.