Five of the six most-visited websites in the world are here, in ranked order: Facebook, Google, YouTube (which Google owns), Yahoo! and Wikipedia. (Number five is a Chinese-language site.) If corporations founded by Stanford alumni were to form an independent nation, it would be the tenth largest economy in the world, with an annual revenue of $2.7 trillion, as some professors at that university recently calculated. Another new report says: ‘If the internet was a country, its gross domestic product would eclipse all others but four within four years.’
That's from this London Review of Books piece by Rebecca Solnit. The October, 2012, research report on which the claim is based is here, based on survey data. Solnit's piece is interesting throughout, including a discussion of parallels and differences between the tech boom and the Gold Rush.