Are sleep states effective in data centers?

While sleep states have existed for mobile devices and workstations for some time, these sleep states have not been incorporated into most of the servers in today's data centers. High setup times make data center administrators fearful of any form of dynamic power management, whereby servers are suspended or shut down when load drops. This general reluctance has stalled research into whether there might be some feasible sleep state (with sufficiently low setup overhead and/or sufficiently low power) that would actually be beneficial in data centers.