One of the major challenges in the US National Airspace System (NAS) today is improving the decisions made when adverse aviation weather occurs. Major increases in the usage of high altitude en route airspace by regional and corporate jets, coupled with greater use of "secondary" airports by low cost air carriers, have dramatically increased the complexity of operating the NAS during bad weather. One potentially powerful approach to improving decision making is to explicitly combine aviation weather information with aviation system information to create an integrated weather/air traffic management (wx/ATM) system that improves the productivity of the NAS operators. However, it will not be enough to be able to develop the technology that could make system improvements possible; it has now become increasingly important to demonstrate quantitative user benefits for any new initiatives. In this paper, we discuss the implications on the development and testing of wx/ATM systems of the need for a successful operational benefits demonstration of the new capability. The paper proceeds as follows. In the next section, we discuss how an integrated wx/ATM system differs from the "conventional" aviation weather decision process. Section 3 describes current efforts by the FAA and the Office of Management and Budget (OMB) to appropriately consider operational benefits as a factor in investment decision making. Section 4 discusses key elements of an "operational benefits centric" approach to wx/ATM system development and testing. Sections 5 and 6 discuss two contemporary examples of integrated wx/ATM systems in the context of section 4. The paper concludes with a summary and recommendations.