Arnaud,
I believe what I have to do now is to build some solid queries to explore our activity log...
Unless I'm mistaken, I believe that you may have misread Richard's advice. (Correct me if I'm wrong, Richard.) His recommendation:
I stress accounting log reporting because it is the very best, detailed handle on what your clients are throwing at the server
Accounting log records are comma-delimited records written to a flat file called dsmaccnt.log, assuming that you have accounting turned on. If you don't, I would recommend that you turn it on now...
The accounting log records give a very detailed, session-by-session picture of the activity between the server and clients. It will be easier to parse and process than what you can get out of the activity log.
Ted