One of the most consistent, powerful and philosophical ideas which has run like a silk thread through the short and erratic history of the development of computer aided architectural design is that of user participation in the design decision-making process. It is not an idea with which the architectural profession is particularly comfortable but it is, the authors claim, one which is central to the professional ethic and, therefore, to be its ultimate survival. Design decision making is, if addressed properly, a hugely, complex multi-variate, multi-person process on which precious little serious research has been focused. In the late 1960's the Design Methods Group in the USA and the Design Research Society in the UK formulated paper based models of the design process and anticipated, in some regards with un-nerving accuracy, the way in which the application of information technologies would impinge beneficially on the process of design decision-making and, therefore, on the quality of the built environment. One concept expressed at that time was as follows: the application of computers to the modelling and prediction of the cost and performance behaviour of alternative design solutions allows subjective value judgements to be better informed and more explicitly audited, and that such subjective value judgements should be made by those most affected by them, i.e. the future owners and users of buildings. This paper is devoted to the critical re-examination of this concept, on the seminal research and development which has kept the notion alive over 30 years, and, how the current advances in multimedia, virtual reality and internet access make its ubiquitous adoption inevitable: in short, Media in Mediation.