This topic is now published on the MSDN Library at Versioning SQL Azure Schemas by Using Federations.
The bottom-line idea of the topic is that because SQL Azure Federation members can have different database schemas, therefore you can use this in order to upgrade your schema incrementally. This can be handy if you have an application with multiple customers, or a multi-tenant application: it enables you to roll out new features selectively, instead of all at once. You might want to do this if your customers vary in how quickly they wish to adopt new features. And it could be a useful way of validating your testing: just go live with a small subset of customers, and the impact of any bugs will be more contained.
I'd love to hear about your experiences using this scenario: is it easy to use? Are there glitches in the process that Microsoft could improve? Our software development gets driven by customer requests and experiences, so let us know what you think.
This topic describes one scenario that comes from being able to have different database schemas in federation members. But perhaps you have discovered a new scenario where you can use this feature. If so, we'd love to hear about it.
As an experiment, this was first released on the Microsoft Technet Wiki, at http://social.technet.microsoft.com/wiki/contents/articles/7894.versioning-sql-azure-schemas-by-using-federations.aspx. As a wiki article, you can easily edit it and make changes to it, unlike with MSDN articles. I'll be monitoring the wiki article for updates and comments, so that I can incorporate them into the MSDN version.