One, I would be surprised if a lot of people had more. Though, in the future, when all game consoles, computers and phones are in one device, maybe it'll be like home computers where everyone has several. Or else they will be implanted in our brains.
"The world has been printing books for 450 years, and yet gunpowder still has a wider circulation. Never mind! Printer's ink is the greater explosive: it will win." - Christopher Morley, "The Haunted Bookshop."