1. A method for mitigating an impact of a data center thermal event, comprising: assigning importance levels to host server computers in the data center, the importance levels based on how powering down the host server computers will impact customers using the host server computers; detecting a thermal event in the data center; using the assigned importance levels, powering down the host server computers in a priority order so that less important host server computers are powered down before more important host server computers; detecting that the thermal event has passed; and using the assigned importance levels, powering up the host server computers in accordance with the priority order so that more important host server computers are powered up before less important host server computers.