Facebook nixes virtualization, eyes Intel microservers (techworld.com.au)

Why would their web servers be virtualized" With the exception of Netflix, The cases I see being made for virtualization is that you have many services that do not need a full server. Virtualization allows you to disassociate these services from hardware, decreasing total hardware outlay and allowing for failover in the event of hardware failure.

And in Netflix's case, they seem to be more interested in outsourcing hardware than virtualization.