Over in his IP Babble blog, my friend and colleague William Henry talks about putting the "service" into your services. What he wisely suggests is to avoid going through a hop or hub to perform conversions, and instead build them into the endpoints themselves. This works especially well when you employ the Chain of Responsibility pattern to create an interceptor-based design so that conversions like these are relatively easy to add, even into an already-running service.
Many enterprise service developers have fallen into the trap of believing the EAI snake oil salesmen who preach that hubs are beneficial. Such hubs have proven themselves to be overly costly to put in place, hard to deploy, hard to maintain, expensive to extend, and capable of only glacial performance. Instead of falling into the hub trap, make your endpoints smart and capable so that your applications can communicate without hubs.
Obviously this won't work if you're building a mashup or are otherwise composing services over which you have no implementation control. But in the enterprise, you normally have such control, and it only makes sense to take advantage of it whenever possible.