Andrew Whitworth wrote:
When the UN APDIP donated their library of ebooks to our project, we included links to all the original PDF versions on the UN website. You can see all these books at [[Category:APDIP Books]]. All of those ebooks also include information about the original authors, and other meta-information to help direct interested readers back to the UN. An important point to make here, however, is that the links to the UN website are not considered to be links "for profit", and so we don't consider them spam or anything like that.
-- Andrew Whitworth
I don't think that the issue of external links on Wikibooks or any other Wikimedia project really has to do much with wheither the link is "for profit" or not. The main issue is if the link has any relevance to the material that it is related to. A Wikipedia article (or even a how-to repair manual on Wikibooks) about the Ford Motor Company certainly can have a link to the official corporate website... and be considered a high quality link.
In the case of the UN APDIP books, a link to the original PDF files is certainly relevant as it is the original source material, and you are maintaining academic integrety by noting the original source of the text. In a similar vein, if this offer to have the book on Wikibooks were to happen or even if it were just used as source material to create a very different book, its use as a bilbliographic reference certainly is very justified.
The problem with link spamming is that 300 links for Viagra on a page about Quantum Mechanics is completely irrelvant to the topic under discussion. A sexual health Wikibook, on the other hand.....