Role Based Access Control (RBAC) is the new permissions model in Microsoft Exchange Server 2010. With RBAC, you don't need to modify and manage access control lists (ACLs), which was done in Exchange Server 2007 and earlier.

You can read more about it at Exchange Team Blog: http://msexchangeteam.com/archive/2009/11/16/453222.aspx

Technet Reference to Understanding Role Based Access Control is another great reference: http://technet.microsoft.com/en-us/library/dd298183.aspx

Feel free to add your thoughts and comments.