I’ll throw out my two bits and see what sort of discussion it generates…
B2B and EAI are conceptually equivalent. As a group we need to stop distinguishing between EAI (often referred to as A2A) and B2B. It’s all integration. The same set of tasks are involved (data access, transformation, routing, transport, etc.).
Some may offer that managing partner profiles makes B2B unique and should be considered separately. I’d counter that managing partner profiles is essentially the same as configuring an adapter. Just like a DB needs to be told what host, instance, and tables to use, so too does the “partner” adapter need to be told how to communicate with partners.
eAI Journal editorials also take this point of view. The term “EAI” is beginning to be accepted as the general term for integration, regardless of whether the integration is connecting apps within a company or is done between two companies. We hardly see the term A2A in the media any more.
But I suppose that wasn’t really the question at hand–it was probably more along the lines of when to use Enterprise Server and when to use Integration Server. The answer, as usual, depends on what an integration is specifically doing. In my opinion, most all integrations should be done using Integration Server. The value-add of ES is steadily decreasing and the wM product direction clearly favors the IS environment.
In other posts I’ve offerred that I believe the pub/sub facility of ES is the one remaining advantage over IS. I believe this too will change (it should change). Pub/sub makes sense for some integrations. But most times pub/sub is not necessary and is used simply because it is there.
That’s the end of the show. Please exit to the left of the soap box. 
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