[pkovak]

Yes, I think it would be better if the cover worked like cover on paper books, you open one side and read, but the cover is still "attached".
What you can do and it could have pretty good results, is take some small book or simply some block of material with dimensions close to eReader and make several types of covers from hard paper. Price of that is virtually zero, and you can experiment with it to see what is good or bad idea. It can't give you final solution, but it can discard some of them or tell you what can be good.

As I said, I am for using the device without taking it out of cover. But it has to have two things in mind:

1) One side easy to open, so you can work with it like with a book. Probably magnetic lock. But it still should not open whenever it wants, only when user want.

2) Two ways of attaching device to cover - one temporary, like putting eReader in a bag, for people who decide they want to take the device out for reading. And the second one where we can firmly attach eReader to cover, so it can't drop out by accident, even when user is reading and the whole package starts heading for a ground in a hurry.
Basicaly, there are two environments people will use your book: safe and unsafe. Unsafe environment means bus, walking on the street, etc. When you are reading "just one last chapter" in a bed, it's relatively safe environment. You don't need cover there most of the time. In unsafe environment, I would worry about my eReader quite a lot if it was not in cover. It can't do miracles, but it can help a lot.

Personally, I think the cover could be made from two types of materials: one sturdy, that could prevent crushing, and second one softer, to soften the impact. Like leather, but with alluminium or hard plastic inside, so it's not visible, but do it's work. Now if I want to read, I simply open one side and read it like a book.

Another idea that can help you with locating worst problems: talk to people who do eReader servicing when someone send it back for repairs or new one. They should have pretty good idea which parts are broken most of the time and in some cases even how it happened. Even when they don't use eReaders themselves, they have probably seen more broken ones then most users.