Just a quick development note.  This is obvious, but had me fooled for a little while.  Simply put coldfusion does not return an error via AJAX if the onError method is set in the Application.cfc file.  This is obvious because the error is being handled elsewhere.  Nonetheless, if you are in development mode using AJAX and have the onError method turned off then you can view your the errors that are thrown in the cfc being called remotely.  Very nice and very helpful.  Then you go into production, and, like any good developer you set up all of your error handling.  But.. But there is a problem with one of the ajax calls to a cfc.  No big thing, just inspect it in Firebug or Safari’s Web Inspector (or even IE8′s new developer tool if you can make it through all the security alerts).  But you don’t see an error, just an empty call.  Not only was an error not returned, nothing was returned.  Well, it’s just because your error handler template has done something else with the error.

So choose to tackle the error in whatever way seems fit.  But the console will not return Coldfusion/AJAX errors while the onError method is running.