My new team just released R12 of BizTalk Services (the umbrella codename for Identity, Messaging and Workflow services in the Cloud).
Clemens has a detailed blog post which covers the new features.
More information about services and the SDK can be found at http://labs.biztalk.net. Anyone can sign up for an account and start using the service right away (however don't forget we are still in beta).
P.S. I know it confuses a lot of people - but the service is not actually BizTalk Server. Zero knowledge of BizTalk Server is required to us the service. The BizTalk brand was used to denote 'systems integration' functionality. I'm guessing that in the medium/long term you'll see us adopt another brand for this service.