ethics of trackback to book?

Hi all, I just wrote a blog entry on a book that Packt is publishing on the PEAR Installer. In the entry, I linked to the PEAR package for trackback purposes, but this got me thinking - is it ethical to link from the open source website to a blog entry on a commercial book? I don't want to do anything that would compromise the integrity of PEAR's open source-ness in this regard, so before approving or rejecting the trackback, I'd love your opinions on what I should do. Thanks, Greg P.S. the blog entry is at http://greg.chiaraquartet.net and is basically a "release announcement" of the book with links to both the publisher and to the PEAR Installer