Heads up: If things go as planned, the BizTalk Services cloud will be unavailable for a few hours during the day on Tuesday 7/15 (U.S. Pacific Time) since we're doing an update to the services and to the SDK. I will post an update with the exact time window some time on Monday. Once we're back up and have verified that everything is working as intended we'll let you know about it and tell you what's new.
Applications built on the R11 release (the release currently running in the data center) will have to be recompiled (and in some instances slightly changed) against the new R12 release's assemblies to run with R12. We've done some protocol adjustments in R12 that make this necessary - mind that we're still in "experimentation-only preview" mode here. Theory suggests that some compiled R11 applications will work against the R12 cloud, but it's not a combination we're explicitly testing as of yet. We obviously have that sort of backwards compatibility on the radar (it's SOA, should be easy, right?) but it'll likely take us a couple more revisions before we're happy enough with the baseline protocols.
[Update: The switch to R12 will happen between 1400-1600 PT/2300-0100 UTC. More later]