Note: Every entry in Trace.log is doubled and the trace is also written to the console. Why that?

  <system.diagnostics>
    <sources>
      <source name="Microsoft.Practices.CompositeUI.EventBroker.EventTopic" switchName="TraceSwitch">
        <listeners>
          <add name="textfile" />
          <remove name="Default" />
        </listeners>
      </source>
    </sources>

    <switches>
      <add name="TraceSwitch" value="Verbose" />
    </switches>

    <sharedListeners>
      <add name="textfile" type="System.Diagnostics.TextWriterTraceListener" initializeData="Trace.log" />
    </sharedListeners>

    <trace autoflush="true" indentsize="4">
      <listeners>
        <add name="textfile" />
      </listeners>
    </trace>
  </system.diagnostics>