When Dublin (now Windows Server Appfaric) was close to being released, there was lot of talk around the speculative demise of Biztalk. Some of the key differentiators identified at that time were Mapper tool and ability to resume message flow using persistence data store. At that time, I wrote that it will be matter of time that these differentiators between Biztalk and Dublin will fade away (check the comment section of http://geekswithblogs.net/cyoung/archive/2008/10/15/125848.aspx). Current Avatar of Dublin aka WS Appfabric , provides the ability to persist data and supports resumption of messages. “AppFabric Connect” feature, that is part of Biztalk 2010 installation, exposes Biztalk mapper and LOB directly. So to be used with workflows, that can then be hosted on Windows Server Appfabric which in turn is part of IIS. Light weight applications does not need heavy weight Biztalk database anymore. Low latency scenarios can now easily be constructed using IIS hosting using Dublin.
Since this feature is part of Biztalk 2010 installation, Biztalk license is needed to use this feature. In future this can and will change. It will then be possible to create custom WF that can be persisted to a DB and exposed as WCF endpoints, while mapping .net types using Biztalk with same set of mapping functoids that are part of Biztalk world. And all of this will be free!