If you are running Hyper-V or Virtual Server in a clustered configuration – you need to be careful about just shutting down a cluster node. If you need to shutdown one of the cluster nodes you need to first open the cluster manager and select to either failover or offline each of the virtual machine resources on the cluster node in question.
The reason why you need to do this is because if you just shutdown the cluster node (without first offlining or moving the virtual machines) Hyper-V and Virtual Server will try to save state or shutdown the virtual machines as part of the shutdown process. However the cluster service will start these virtual machines up again because they are supposed to be online. The net result is that the cluster node will shutdown with running virtual machines – which will result in an unplanned failover of the virtual machines in question.