Pretty old but still handy configuration.

IIS + ASP.NET only.

http://msdn.microsoft.com/en-us/library/ms733025.aspx

<configuration>
   <system.diagnostics>
      <sources>
            <source name="System.ServiceModel"
                    switchValue="Information, ActivityTracing"
                    propagateActivity="true">
            <listeners>
               <add name="traceListener"
                   type="System.Diagnostics.XmlWriterTraceListener"
                   initializeData= "c:\log\Traces.svclog" />
            </listeners>
         </source>
      </sources>
   </system.diagnostics>
</configuration>