From http://blogs.msdn.com/windowsazure/archive/2009/03/18/the-windows-azure-malfunction-this-weekend.aspx
For continued availability during upgrades, we recommend that application owners deploy their application with multiple instances of each role. We'll make two the default in our project templates and samples. We will not count the second instance against quota limits, so CTP participants can feel comfortable running two instances of each application role.