Active Directory Performance Analysis
Prior to Windows Server 2008, troubleshooting Active Directory performance issues often required the installation of Server Performance Advisor.
Those who came to rely upon this tool will be happy to know its functionality has been built into Windows Server 2008 and Windows Server 2008 R2.
This performance feature is located in the Server Manager snap-in under the Diagnostics node and when the Active Directory Domain Services Role is installed the Active Directory Diagnostics data collector set is automatically created under System.
David Everett posted an article on Microsoft Directory Server Team Blog which lights up all the details about this tool.