Check out this link a friend of mine sent: ESB vs. BizTalk Debate Heats up in Barcelona. Dave Chappell writes:
While giving a presentation at the Enterprise Architect Summit in Barcelona on the subject of ESB and other SOA-related infrastructures (see Resources), I got into a public altercation with a couple of Microsoft guys who were in the audience. It turned into a pretty heated debate over core architectural fundamentals, which we hammered out in front of an audience of about 75 unsuspecting conference-goers. I have to say that in all my years of public speaking, this sort of spontaneous public debate has never happened quite like this. The conversation that ensued brought to light some important issues regarding fundamental differences between the use of an ESB as the foundation of building a service-oriented architecture vs. using a combination of BizTalk and WCF (formerly known as Indigo).
There is a webinar recording available.