The facility Facebook's rumored to be behind is under right now construction and will cover 117,245 square feet in Prineville, Oregon. Unless some seriously innovative construction techniques and types of hardware are employed, it's sure to cost more than $100 million, and data centers often carry price tags along the lines of $500 million.
Then, when the construction's done, Miller writes that it will take about 35 people to staff the data center.
So Facebook does indeed seem to be making a major move. We'll try to relay more details as they become available.
