According to a rumor on the Internet, Facebook may be rolling out a new data center filled with servers using ARM CPUs rather than the more traditional chips from Intel and AMD. ARM chips are less complex than x86 systems, and ARM is ubiquitous in mobile computing environments. The simplicity of the architecture makes the systems far more energy efficient, which is a pretty serious concern when you’re a company like Facebook building a new data center.
There’s no real meat to the rumor, other than speculation. No links to back up the speculation, either. So make of this what you will. I think it makes a lot of sense, but that doesn’t make the rumor true.