New Windows Azure Portal let you add up 10 users as co-administrator using Windows Live ID. You just need to add co-administrator Windows Live ID in the “User Management” Section as below:

 

 

A few things to remember:

-       The limit to add maximum co-administrator is 10.

-       Only Live ID are suported. Even though the Windows Azure portal can let your add any non Live ID in the user management section, however when login to portal you can only use Live ID

-       Windows Azure, SQL Azure and App Fabric services are accessed and managed by Co-Administrators:

http://blogs.msdn.com/b/appfabric/archive/2011/07/25/announcing-the-windows-azure-appfabric-july-release.aspx

-       When co-admin uses the site, it is possible that you may not see any App Fabric detials. In my case it took about 24 hours to get the co-admin account working with App Fabric.