The official Stormpath .NET SDK by Stormpath calls the Stormpath REST API which provides developers with a user management infrastructure. Features include authentication, schema-less user data and social media login with Facebook and Google OAuth.
One of the big debates these days when it comes to cloud computing center around portability and interoperatbilty between providers. That is, if you build an application on Amazon's EC2 or Google's AppEngine or Force.com, or store your data on Box.net or Amazon's S3, how hard is it to port your application or move your data to another cloud provider? If you develop on a given platform, how locked-in, or not, are you? And beyond that, could developers benefit from having standardized APIs to develop to without having to learn a new model and interface each time. As you'd expect, there's no easy answer to this.