Microsoft has built a Linux distro, and is using it for their Azure data centres:
"It is a cross-platform modular operating system for data center networking built on Linux" [microsoft.com]
Apparently, the existing SDN (Software Defined Network) implementations didn't fit on Microsoft's plans for the ACS (Azure Cloud Switch), so they decided to roll their own infrastructure. No explanation why they settled on Linux, though - could it be that there is no windows variant that would fit the bill?
On other news, Lucifer has been heard complaining of the sudden cold.