I got it. After reading some of the documentation on DataService.getItem I learned that the "ItemReference" object that is given back extends "AsyncToken". This means you should either bind to the "result" property of the ItemReference or add a responder to it (i.e. itemRef.addResponder).
Then once the data is retrieved your "result" or "fault" methods (from the mx.rpc.IResponder interface) will be invoked.