My career in ColdFusion, JRun, J2EE applications has very much been in the server side since I joined Allaire back in 1999.  As a group of consultants with Allaire, we travelled the world helping clients to trouble-shoot and improve performance of ColdFusion and JRun applications.  A large part of that involved load-testing applications and capturing metrics from those tests and then homing in on bottlenecks identified.  In that process we would capture variables used, SQL queries that ran etc.  The modus operandi would be to record various load tests via a browser recorder and then enhance that by randomizing variables passed in.  With applications based on Ajax-Flex that becomes much more difficult and we are in the throes of developing an efficient mechanism to do that and I will blog about it as we go forward. 

If anyone wishes to share how you are dealing with this, you are welcome to comment on this thread and there is one more point I would like to make and that is that we should never deploy any applications to production without load-testing them first.  I blogged on that subject, here.