Facebook has been able to quantify energy efficiency gains of 38% for new servers conforming to the specs of The Open Compute Project, said Matt Corddry, Director of Hardware Engineering at Facebook, speaking at the Open Server Summit in Santa Clara, California.  Moreover, the new servers deliver a 24% cost savings compared to generic OEM servers. 

The Open Compute Project, which Facebook launched in April 2011, has resulted in vastly simplified Compute Servers, Storage JBODs and an innovative Open Rack System.

 Source: http://www.convergedigest.com/2013/10/open-server-summit-open-compute.html