So far, they seem quite pleased by the results of the data center design:
The result is that our Prineville data center uses 38 percent less energy to do the same work as Facebook’s existing facilities, while costing 24 percent less.
Since I know very little about hardware design, I'll ask the first really stupid question that came up as I was reading the materials:
What is a "vanity free" server?
Meanwhile, the various media seem to be trying to build this up into a battle between Facebook and Google, but I find that claim hard to swallow. As Facebook themselves say, their engineering team has historically been a very open team, releasing infrastructure such as Cassandra back to the world as they built it.
Thank you, Facebook, for releasing this information; the world is now a little bit smarter.