After I read the summary and saw this "Apress, to offer the ebook version for free, believing (strongly) that it would promote sales of the paper book.", I had to post just to say I totally agree. I much prefer a paper back copy (and not a loosely bound pile of A4 printouts) for studying material at leisure. Especially when I'm dipping into a new topic and want a good overview rather than the stage where I'm piecing together bits of knowledge from the net.I really like the typesetting and format of the Apress books so after a couple of days of reading through their Pro Drupal and the PHP patterns book via the PDF I decided I really did want these books and went off to pick them up from the bookstore.
Whilst I agree that there are some that always will just take the stuff, for those that can afford it many will buy it if they want it. I'm going to get the PDF anyway from something like ebookee or even google so just give up already and promote it on your site and take the print sales as they come. Those that really want this book will buy it. Fair play to the author.