For debugging webservices, the first tool is obviously http monitors like Fiddler or Ethereal(WireShark). Almost everyone who has developed a webservice knows that. It is also true that these tools works well when your webservice is not hosted locally. There are of course other tricks to make it work. But, when it comes to Adobe flex, the challenge is not over even if you got the SOAP response xml back from server. You have to bind it appropriately to see the results. That is where the top secret *j/k* API is useful.
Use "mx.utils.ObjectUtil.toString(resultEvent.result)" to see the structure of result object and get your binding expression correct. Also, see my upcoming post about tracing.