This week on the internet:
Controversial post from The Ethicist, followed by some interesting points on both sides, notably by Nathan Bransford and John Scalzi.
I think part of the controversy is about what you are paying for when you buy a book. Are you buying a product or are you buying the content in the product?
Those arguing for a full payment for each version of the book that you buy are often arguing the product approach: it's a separate product each time; each product has production costs; each product is unique.
Those arguing for a free e-book version after buying a hardback or paperback are often arguing the content approach: they are the same words regardless of version; if you're buying the right to read those words, does it matter what version you read them in?
I've also seen a few people who are looking for a middle ground: buy a hardback or paperback copy and get the e-book at a reduced cost. I think if the author and all the other people involved in producing the book are amenable to this it isn't a terrible idea. If they are willing to give you the e-book for the cost of production (which it would appear is more than nothing), perhaps even the cost of production plus a little something but still less than the original cost, then that's probably a good compromise.
Perhaps some books could come with a cd or website code or something along those lines (tucked away and sealed so you would know if somebody has tampered with the book) that would contain access to an e-book version. And those books could be sold at a price higher than the plain book but lower than the price of that copy and the e-book copy combined.