Modern Perl, the book, is Available.
modernperlbooks.com
modernperlbooks.com
Which part of the book made you think that? I'm actually curious, since after a quick browse through, I see a tutorial / well written language reference mostly...
Where did all those pages go?
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.
If I can write two books in a year and a reasonable wage for my experience and expenses is $80,000 a year, each book needs to earn about $40,000 to justify me continuing to write. Divide that by the number of readers to figure out the amount of profit I need to make per unit.
I can justify giving away the electronic version and soliciting donations on theory that free redistribution from countless readers will reach a much larger potential audience for print sales and donations than I could possibly reach, especially with my marketing budget. Besides that, doing so appeals to my sense of ethics. Many, many people contributed to making Perl 5 and many, many people helped me write the book.
http://danonline.net/modernperl
Thank you so much for writing this, chromatic!