One issue with highly redudandent data centers is the failure modes are "interesting." You don't want to shutdown due to a single UPS failure, so you don't use something simple like PowerChute Plus. You most likely don't want to shutdown based on any automatic signal. However, you do want a way for an operator to gracefully shutdown a lot of equipment quickly when the decision is made.
The old Deltec stuff was good about this. They had it so that a server daemon would notify different groups at different stages. Power lost->notify group A (Printers, PCs) Low battery->notify group B (Secondary servers) Dead battery->notify group C (Primary servers, comms) They also had different outlets on different "groups", so if a device wasn't able to understand the network alert (the routers and firewalls don't have agents), they could be terminated as a part of a group. Deltec got bought by somebody and I'm sure a lot of this stuff has changed since I last looked at it, but it was a good design. -- Eric A. Hall http://www.ehsco.com/ Internet Core Protocols http://www.oreilly.com/catalog/coreprot/