An electronic book that works?

[Alex]

No, not if it is in a DRM format. For books in non-DRM formats you can share all you want (though not directly from the Kindle)

Barnes & Noble's new reader, the Nook, does have a very limited sharing capability. Every book you buy through them you can loan to another Nook owner. While you have it loaned out you do not have the ability to read it on your Nook.

However, it is very limited. Each book can only be loaned out once in your ownership lifetime and for only 14 days at most.

That said, with the Kindle you can have up to five Kindles linked to the same account and any book on that account can be downloaded to any or all of the Kindles. Since only one payment account exists per account, though, this means somebody will have to trust other people if they want to link accounts.

But since I do have two Kindles and Lani recently wanted to read a book I had already read on my Kindle, I just gave her my old one and she can read it on there. If she wants to buy new books that is fine since we're financially comingled and I trust her. If she does so, I'll have access to that book as well on my Kindle.

There is currently no concept of a "used book" in the eReader marketplace. I have advocated for it (and it could even be done so that the publisher/author gets a cut of the resale) but I know of no seller planning to do such a thing and I'm guessing the publisher would **** bricks at the thought. That said, because etext versions tend to be significantly cheaper than paper versions of the same thing I think you'd still generally come out ahead on price buying it cheaper up front than buying paper and selling it to a used bookstore.