How do we know in advance about service downtime by a planned maintenance?
Windows Azure is designed to avoid downtime for customer applications, storage and service management capability during maintenance activities on the Windows Azure platform. Our availability commitment applies to customer applications which use a minimum of two role instances. Customers with single instance applications can learn about Windows Azure best practices for mitigating downtime by reading this MSDN article entry. The Windows Azure SLA is documented here
In the event of an unplanned service disruption on the Windows Azure Platform, status updates will be made