The folks from Alinan have developed a very comprehensive and detailed TCO/ROI comparison tool for the Microsoft Windows Azure Platform. You can access the tool at http://www.microsoft.com/windowsazure/tco/. This tool does an excellent job of calculating the TCO/ROI of hosting an existing application on the Windows Azure Platform as compared to running the application on-premise. In doing this it considers not only the cost of operation but the entire application life-cycle. This includes planning, acquisition, setup and installation, management and support, evolution and retirement of the application. In the case of an existing on-premise application it also considers the cost of migrating the application.