Many people know that we run several customer test programs, and as part of those programs, we have customers that are running pre-release code in production. Those programs and deployments are closely supervised, monitored and supported. Note however that a public Beta release (such as this one) is NOT such a program, and you SHOULD NOT install Beta code into your production environment!
Exchange Server 2010 will extend your Active Directory schema and it will change permissioning on Exchange organization and other objects which, in this early stage, might cause interoperability issues if Exchange organization is not ready for it.
We want to strike a balance between releasing early builds so that our customers can see the product and give us feedback and ensuring that our customers have a good experience with the product. When our instructions about an early build being for testing only are ignored, customers can have a bad experience and it makes it harder for us to decide to release early builds because we don't want those situations to happen.
We are glad to see excitement around new Exchange 2010 features, but please - test them in the lab only!