We needed a really light weight ESB and we were evaluating Mule, ServiceMix and finally decided to write our own Spring based service bus. And it ended up working great for us. At that time, the Spring Integration was just being developed. I was looking into the Spring Integration and looks like it is very endpoint / channel based. We wrote a component based service bus, that would just intercept, transform and invoke a service. Spring Integration is neat and flexible, but I’m not sure how the polling channel model would perform. Also we have services that communicate synchronously, but I’m not sure if there is a way to define a request/response type of architecture with Spring Integration. Looks like it is necessary to implement an input and output channel for every messaging pattern like transformer, router, etc.