Who Buys Books?
Tim Bray on buying books:
This works because Amazon doesn’t mind multiple devices at once having access to a book; and because our “Amazon identity” is a lightweight shopping-context thing, not like a “This is really me” Facebook or G+ identity.
This highlights a very important thing about Internet identity: identity is not something that can be modeled easily, and it’s certainly not something that’s unique, whatever Mark Zuckerberg may think.