
Apple?
They are in the process of building a new data centre in North Carolina.
Facebook, don't they use their own?
Supermicro says it has shipped 30,000-plus servers into a "Fortune 100" company’s Silicon Valley data centre. The company said its customer had deployed that number of disaggregated MicroBlade systems at "one of the world’s" highest density and energy efficient data centres. The data centre has a Power Use Effectiveness (PUE) …
Intel's formerly vacant chip fabs in Santa Clara [0], maybe? There's an Intel white-paper describing their high density sub 1.07 PUE design [1].
Nuclear because their hot aisles can reach 54 degrees Celsius.
[0] http://datacenterfrontier.com/intel-data-center-new-heights-efficiency/
[1] http://www.intel.com/content/dam/www/public/us/en/documents/best-practices/intel-it-extremely-energy-efficient-high-density-data-centers-paper.pdf