BizTalk server was taunted as Microsoft's Web Service Enablement platform but I see more and more solutions where the designers feel the need to introduce web services layer on the applications being connected using BizTalk. In my opinion, BizTalk server should be used to connect applications through their native API.. If you already spent the money on BizTalk, I would like to see getting messages in and out of BizTalk with minimum fuss and use BizTalk server's excellend capabilities for dynamic transformation and routing along with BizTalk servers' web service publishing capability to web enable these applications via BizTalk
In fact if each application you are connecting is already web service enabled, you get into rapidly diminishing returns on your BizTalk investment unless you need BizTalk for correlation or business rules. In fact if you enable web services on each of the connected applications then WCF used with channels and routing makes BizTalk messaging and content based routing redundant.