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.
I use the same scheme as Tim when it comes to buying Kindle books – right now I only share with my wife but the kids will get on board when they’re old enough – and that’s OK because our Amazon account reflects the family unit as the customer: when you buy a book or a movie or, for that matter, a TV or a car, you don’t buy it as yourself but as a member of a group. Some companies may have thought otherwise all these years, but it’s always been the case.