Sorry I don't feel free to give details, but basically his book book was for sale, then he made it available for free as HTML, and he claimed the drop in sales on Amazon the next day was quite distinctive. All subsequent versions were only available for a price, e-book or otherwise.

Still, looking at the anecdotal evidence, I think that some books, books that work best as references, will loose sales if there's a free online version since reading it online works so well; it may be better than any other version. If a book is more complex, requires more close reading, a physical copy (or at least a better formated PDF) would be preferable to some free HTML version.

However, that was before iPad. As ebook reading experiences away from the computer get better and better, there will be fewer cases where I'll by the physical book if a free ebook is available.