1. A computer-implemented method for providing computing resources, comprising: receiving, by one or more computer systems, a request to provision a number of virtual computer systems for a customer of the virtual resource provider using dedicated hardware, wherein fulfillment of the request requires allocation of a first amount of capacity for the number of virtual computer systems; as a result of the customer having specified use of dedicated hardware, dedicating, by the one or more computer systems, a group of hardware devices, the group of hardware devices comprising a number of hardware devices that is greater than a minimum number of hardware devices sufficient for the allocation of the first amount of capacity, in a manner that prevents virtual computer system instances from being implemented for other customers of the virtual resource provider using the group of hardware devices and that fulfills one or more conditions that include a condition on a second amount of capacity of the group that can be used upon provisioning the number of virtual computer systems; provisioning, by the one or more computer systems, the number of virtual computer systems using one or more hardware devices in the dedicated group while, as a result of the condition on the second amount of capacity, leaving capacity for at least one additional virtual computer system in the group; and providing, by the one or more computer systems, to the customer, access to the provisioned number of virtual computer systems.