This paper attempts to identify the necessary features that make the difference between a KBS which will remain in its authors laboratory and a system that becomes really used, i.e a product. We illustrate these features with a prescribing optimization decision support system, called OPADE; this software is being developed in the setting of the AIM initiative and definitively aims at becoming a product used in daily clinical practice in several European countries. While developing the system, we purposedly take a pragmatical, product oriented approach, which may hurt by its simplicity. But it is our feeling that the only future of KBS is to prove that, even if simplified, it does work now.