The BizTalk Labs have delivered a new part, a hosted Workflow Service, now it is possible to create a workflow and host it in the "cloud". we can use the ISB (Internet Service Bus, instead of Enterprise) to send messages across the internet. Combine this with authentication and authorization and we have a powerfull orchestrator.
Get the BizTalk Services SDK, it will contain a "watchdog" sample workflow, this workflow will ping a website, and will report the status to a chat client (MultiCastSample). To create this, there are some new Activities to use from the Toolbox, e.g. a CloudDelay, a CloudIfElse, etc.
From the workflow.biztalk.net site (after creating some InfoCards for authentication) we can create our own Workflow 
(by copying the XOML and rules from Visual Studio) into the site. This is our workflowtype, and in the UI 
from the BizTalk Labs, we can create an instance of our workflow, and we can start the instance. Now the workflow is checking the site every 30 seconds, and sending messages to the Chat client
Finally we can start the client.
So this sample allows us to subscribe to (chat) messages coming from the "cloud" and we've started a WF process, which sends messages to our cloud. So the whole proces of Orchestrating service calls, authentication and authorization, connecting through firewalls are all done by the BizTalk Services SDK.
Don't forget to suspend the workflow, it will keep on running...