As energy costs and energy used by server farms increase, so does the desire to implement energy-aware policies. Although under some metrics, optimal policies for single as well as multiple server systems are known, a number of metrics remain without sufficient knowledge of corresponding optimal policies. We describe and analyse a model to determine an optimal policy for on/off single server systems under a broad range of cost functions that are based on expected response time, expected energy costs, and expected wear and tear costs. We leverage this model in the problem of routing jobs to one of two servers to show a range of non-trivial optimal routing probabilities and server configurations when energy concerns are a factor.