Last week, the Azure team released a cool new feature: support for a DAG Witness server inside an Azure VM. With the latest version of exchange, you can configure automatic data centre failover. But to do that, you new require three physical sites. However, according to Microsoft, many customers only had two physical sites deployed. This is where Azure comes in, since these clients can use Azure as their third physical site. This provides a cost-effective method for improving the overall availability and resiliency of their Exchange deployment, and requires no up front capital expenditure.
OF course, deployment of production Exchange servers is still unsupported on Azure virtual machines. But I can't help thinking that in due course we'll see this restriction changed. MS kind of hint that by saying; "Stay tuned for future announcements about additional support for Azure deployment scenarios.".
Yet another cool scenario available to Azure customers today . For more details on how to do it, see the TechNet article at: http://technet.microsoft.com/en-us/library/dn903504(v=exchg.150).aspx.