Hmmm...(Just to tick HarryT off,
)
What would it take?
How many of you have 3G/4G/Wifi enabled book readers? Hands high!
All you would have to do is to modify the systems software to brick the machine if the "phone home" piece of software is disabled. Then, every time you read the book (say, every time you look at the last page), your reader "phones home" and increment the counter on the server. You hit the max number and then the push software deleted the book. Impossible? Amazon already has the push software as part of their contract when you buy a Kindle. iPad?
Not hard at all...Of course people will still pirate...