Wizard-of-Oz (WOZ) simulations are a popular means for investigating the properties of humancomputer interaction. In this paper the findings from a WOZ experiment for evaluating different design options for a spoken dialogue system are presented. In addition to the documentation of the outcomes of this evaluation in terms of standard quantitative measures we also present findings from a more qualitative analysis of the speech data collected throughout this experiment. It is argued that such a combined analysis of all aspects of the human-computer interaction allows for a correct interpretation of the results and their fruitful application in the context of system prototyping.