A while back I made a little .NET app that allows you to view the number of users on your IIS box. I called it IISreporter. You can read more about it and download the app at www.iisreporter.com. It is free so head on over and signup and download.
It is also featured on IIS.net
IISreporter has finally been retired. Retired meaning I somehow did not renew the domain and a wonderful Chinese company now owns it. If anyone wants the code. Let me know.