Me too! Before we used fruitstrap[0] we used DeviceAnywhere. This was a 2U rack unit that contained a franken-iPhone. The hardware buttons were soldered up to GPIO on the DeviceAnywhere.
For those who showed interest in learning more about our infrastructure/automated testing process, if you could drop me an email? gp at our corp domain fb.com.
I don't work on the team anymore, but I can probably start off a thread with the right people involved from Facebook's side.
Here is a post that Jay Parikh (VP of Infrastructure) made about it. http://tinyurl.com/cnvss4v
Our density isn't as high (we have 64 minis) because of cooling and cabling that we designed according to our datacenter cooling standards.
@jurre - If you want to chat about our design, message me and I can put you in touch with our hardware designer.