I like the way Manning sells e-books. They sell PDF versions of their books for significantly less than paper versions and they give a discount when you buy both. Also, their early access program lets you read books as their being written. Readers get the content sooner and writers get valuable feedback as they go. O’Reilly and Pragmatic Bookshelf have similar programs.
I don’t care for the way Wiley sells e-books. For example, they sell The R Book for $110 in paper and $105 in PDF. That’s absurd. The book has 960 pages weighs 3.7 pounds. The difference in what it costs to produce the paper and electronic versions must be far more than $5. And I don’t believe Wiley gives any discount for buying both paper and PDF versions.
I also find Wiley’s license terms unreasonably restrictive. For example, “you … May not move the file to a different computer.” You may download the file directly to up to four computers within 14 days of buying the book. But if you buy a new computer, say six months after you buy the book, you’re not supposed to move the book to your new machine. That means you’re effectively renting the book for the lifetime of the computer you download it to.