I have always understood Azure AD to be like a hosted ADAM. I have seen people now who are talking about joining machines to Azure AD. At first I assumed they meant a virtual machine on Azure running 2012 server with AD deployed, and maybe a site to site VPN enabled. But some are asserting that they are joining to the Azure AD for sign-on purposes, wherever an organization doesn't require GPO, etc.
So is this really happening? AD hosted in the cloud without virtualized server instances as the DC?