The development of new products that satisfy consumers' needs and preferences is a very important issue. To avoid flops, the control of the risks in product innovation and the reduction of the innovation cycles require valid and fast customer's assessments, for determining new products that effectively corresponds to the customer's taste. In particular, the shape of a product is an important factor in the success or the failure of a product. Since several years, in various research fields, many works are dedicated to the design of shapes by the analysis of user's perception. Kansei engineering for instance produced many tools and methodologies in this research area. The work proposed in this paper is in this context. It is based on the use of interactive users' assessment tests to enhance creativity, by the way of interactive genetic algorithms (IGA) for capturing users' responses. A set of parameterized designs, defined with a CAD system, are presented iteratively to the user for evaluation by a graphical interface. This navigation in the design space may converge towards designs that maximize a subjective criterion, given in advance to the user. We describe in the paper the interest of this approach for the design of forms and the setting of design constraints to the designer. The proposed application concerns the design of "innovative" car dashboards (innovative has to be understood here as in agreement, according to the user, with a particular semantic dimension, for instance "compact", handy", ...).