Bobby Woolf recently published a provocative piece titled, ESB-oriented architecture: The wrong approach to adopting SOA. In it, Bobby makes a very persuasive and effective argument for using an ESB as part of a larger SOA strategy. He says:
Clients often want to build only an ESB because that involves a technology challenge without the need for messy business requirements. Building just an ESB becomes an IT field of dreams, where IT builds an ESB and then hopes some SOA will come along and use it. Such an ESB-oriented architecture loses the benefits of SOA. It does not create business value. In fact, it incurs cost without reaping immediate benefit. And it does not align IT and the business. The better alternative to ESB-oriented architecture is SOA-oriented architecture. Do not build an ESB by itself; build it as part of an SOA, preferably one that fits the SOA Foundation architecture that IBM recommends.
I've worked with Bobby for a few years now, and I have learned that he does not make such statements without the appropriate level of understanding. As an WebSphere SOA and J2EE consultant for IBM, Bobby has spent plenty of time in the field seeing it done well and not-so-well. Because of the respect he's earned, this theme has been picked up in the IT press...in fact, Joe McKendrick from ZDNet wrote about it in his SOA column: ESBs: useless as a human appendix?. The Server Side has also picked up on this and wrote a great synopsis: ESB-Oriented Architecture: The Wrong Approach to Integration.
Overall, Bobby has picked up on a relevant and interesting thread with this. I expect to see others following suit.