Software out there that manages this (Score 1)

There's a Seattle based company, Verdiem, who has a product that according to EcoGeek.org "works by providing centralized management of networked computers to shift them into lower power states when they are not being used."

Verdiem: http://www.verdiem.com/
Surveyor product: http://www.verdiem.com/surveyor/default.asp
Ecogeek article: http://www.ecogeek.org/content/view/1270/