Brendan,
I don't know about JADE on Linux, but I can tell you how to get this information using JADE on Windows. Hopefully the same will work on Linux as well.
To get the information on Windows, set the [WebOptions] LogFileName to something sensible before starting your Web Service app.
e.g.
[WebOptions]
LogFileName=e:\cnwdmast\logs\webmonitor.log
Then, JADE logs the all input messages, plus some relevant information following the reply, including how long the message took to process, how long it was queued before processing, and the total number of entries in the queue at that moment.
e.g. from one of our Web Service apps:
2010/10/11 09:53:44.761 01500-157c :
2010/10/11 09:53:44.761 01500-157c : IP address of requestor = 10.96.130.21
2010/10/11 09:53:44.761 01500-157c : Query String = JMTWebService&serviceName=JMTUserInterfaceService&listName=JMTWebService
2010/10/11 09:53:44.761 01500-157c : Http String = <?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="
http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="
http://www.w3.org/2001/XMLSchema" xmlns:soap="
http://schemas.xmlsoap.org/soap/envelope/" xmlns:tns="
http://tempuri.org/" xmlns:s1="
http://tempuri.org/">
<soap:Header><JadeSessionHeader xmlns="urn:JADEWebServices/s1/"><sessionId>6a2ceadbae89d653</sessionId></JadeSessionHeader></soap:Header>
<soap:Body>
<s1:getCarriers></s1:getCarriers>
</soap:Body></soap:Envelope>
2010/10/11 09:53:44.870 01500-157c : Sending reply - elapsed time: 0.114 secs queued time: 0.000 secs
2010/10/11 09:53:44.870 01500-157c : Queue depth=0
Hope this helps.
Cheers,
Kevin