eBooks, unlike pBooks, could be made unique for every download (e.g. subtle changes in punctuation, or certain words).
Unlike music downloads, such alterations in eBooks needn't detract from the enjoyment of the product.
If an illicit eBook turned up on the net, it could be traced back to the original purchaser. They could be asked why it happened, or blacklisted as a future customer; or investigated more thoroughly for other possible infringements.
This wouldn't stop piracy, but it might be a deterrant as each book would need to be 'cracked' separately - unlike a universal crack for a DRM implementation. The work involved would probably be more trouble than it's worth to a lot of 'pirates'.
Just an idea - a dumb one probably - but an idea nonetheless
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