In the first release of SQL Azure, security is limited to SQL Server user accounts. Windows Integrated Security isn’t yet supported. Expect some sort of support beyond SQL Security at a later date.
Because you can connect to SQL Azure with a regular connection string, any existing data access layers continue to work normally. Communication between SQL Azure and applications that are hosted both inside and outside Windows Azure.
If your application works today using SQL Server Express Edition and doesn’t use some of the more advanced features of SQL Server, then your application should work in the cloud with little or no modification.
Although on-premises applications can talk to SQL Azure, latency might make this a less attractive option. The closer your application is to the database, the faster it’ll go. You can reduce the impact of latency by making your application less chatty.
HOW SCALABLE IS SQL AZURE?
In version 1.0 of SQL Azure, there’s no built-in support for data partitioning (the ability to split your data across multiple servers). The initial release is targeted for databases that are sized up to 10 GB; larger databases aren’t suitable for SQL Azure in this initial release, but support for larger databases will be available in future service updates. If you need to perform partitioning, you need to implement it in the application layer.
Let’s turn now to Azure platform’s enterprise services. Known as AppFabric, these services include the Access Control Service (ACS) and the Service Bus.
Source of Information : Manning Azure in Action 2010