On a smaller scale, a common mistake (learned personally by myself) is to have servers on UPS, and if your really stylin', to have workstations on small ups's, but forgetting to have your switches/hubs/modems on UPS. When the power goes out and the systems stays up everyone cheers and you're the hero - until they realize they are no longer connected to the network and can't save. Then you take advantage of the darkness and slink out quickly before the boss finds you.