I found this on a forwarded mail the other day. Its a previously internal only tool. You can 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 with Outlook 2003 version MAPI.
I wish I’d had this tool when I migrated everything from Exchange 5.5 to Exchange 2000. It would have sorted out so many problems…..