Nice insight. Worth reading the entire article for the details:
Facebook is a wonderful example of the network effect, in which the value of a network to a user is exponentially proportional to the number of other users that network has.
Facebook's power derives from what Jeff Rothschild, its vice president of technology, calls the "social graph"--the sum of the wildly various connections between the site's users and their friends; between people and events; between events and photos; between photos and people; and between a huge number of discrete objects linked by metadata describing them and their connections.
Facebook maintains data centers in Santa Clara, CA; San Francisco; and Northern Virginia. The centers are built on the backs of three tiers of x86 servers loaded up with open-source software, some that Facebook has created itself.
Let's look at the main facility, in Santa Clara, and then show how it interacts with its siblings.