Interesting stuff. I don't have too much to say because this is so far outside my scope of expertise. However, I think it's kinda interesting that servers are moving away from the pizza-box form factors. In the tradition of silly names for things, I propose we call these new 2 rack height, one third rack width boxes loaves, after loaves of bread stacked upon each other.

I eagerly look forward to some admin in a datacenter having to pinch off a bad loaf ;p

Are there any manufacturers that sell the exact same models that FB is using? It would definitely be interesting to get a few to play with.