This may not be news to some developers, but it's good for people to know that ESBs are not just for service-oriented architecture. This article explains what proper ESB solutions and SOA architectures are supposed to imply:
A proper services-oriented architecture reuses the service provided by any given system. A proper ESB solution will transform the data from a common services call so that it can be fed appropriately to any resulting system. By using the same call to any resulting system, and transforming the data in flight to the intended system, you begin to reduce the complexity of the environment.
-- Sean O'Shaughnessey
The article also leaves you with some good advice to beware of integration patterns coming from the application vendors instead of the community.