Interesting that it has a SQL backend, I wonder what they are using as an ORM to enable querying in the collections.
We also give scripts full access to the node-sqlserver driver, so they can run their own arbitrary SQL as necessary.
Anyway, looking at the comments in Scott Guthrie's blogpost (http://weblogs.asp.net/scottgu/archive/2012/08/28/announcing...) he also mentioned that they "will also support unstructured storage in the future so if you don't need rich querying you can use that too."
Also, from the comments he mentions they'll be publishing documentation for the REST API soon'ish (as well as "pre-built REST helper methods for Win8/iOS/Android/others").
I got excited for a moment. I've been using Azure for a few years now and I was thinking that this could have been a hint of them offering something more similar to MongoDB in the future. But, then it hit me that he's probably only talking about the Table Storage (Now called Table Service?) which I will never touch again.
With that said, SQL Database (formerly known as SQL Azure), specially with the Federations feature, is an interesting option for LOB applications.