I serve a lot of map services via my arcgis server 9.3. Can I determine somehow which webapplication or desktop clients are using or were using my services? I know that I can view apache access log and by this way execute this task, but I think that it is not most elegant solution.
There is a utility available on ArcScripts - ServiceMonitor - which can let you get at least some monitoring on your services. I have not tested it myself though.
Free apps are Apache JMeter and Fiddler.