Enables system administrators to view and evaluate individual users' usage and experience with Microsoft Exchange Server.

Use the Microsoft Exchange Server User Monitor to gather real-time data to better understand current client usage patterns, and to plan for future work. Administrators can view several items, including IP addresses used by clients, versions and modes of Microsoft Office Outlook, and resources such as CPU usage, server-side processor latency, and total latency for network and processing. Works with Microsoft Exchange Server 2000, 2003, 2007 and 2010.

Source: http://www.microsoft.com/en-us/download/details.aspx?id=11461

Additionally exchange servers can be monitored trough built-in performance tools such as Performance Monitor and Performance Troubleshooter under EMC Toolbox.

Also PowerShell can be used to obtain e.g. top 10 users that are most actively using Exchange Server:

Get-StoreUsageStatistics -Database Database1 | Sort-Object TimeInserver -Descending | Select-Object -First 10 | ft -AutoSize

Get-StoreUsageStatistics -Server Server1 | Sort-Object TimeInserver -Descending | Select-Object -First 10 | ft -AutoSize