Toyama [19] has proposed a "preliminary taxonomy" for classifying computing projects as a way of separating sustainable computing efforts from unsustainable ones. In this paper we explore the feasibility of Toyama's taxonomy. We begin by describing how we revised and developed his taxonomy to make it more practically useful and then conducted a pilot study where we used the revised version to evaluate four computing projects. The pilot study was then used as a foundation for further discussing and developing the revised taxonomy into yet another, third and final version which we have chosen to call the Sustainable Computing Evaluation Framework (SCEF). While our proposed framework (SCEF) is more practically useful than Toyama's "preliminary taxonomy", there are still challenges that need to be addressed and we end the paper by suggesting where future efforts could be focused.