Simon Owens discusses the merits of free content in general and the Creative Commons license in particular here on his blog. I always have been and continue to be a huge advocate of free content because I see what it can do to help drive sales of the main product. We started with sample chapters, and that's a no-brainer now for any book, but we've also done our share of complete works accessible online at no charge (e.g., Naked Conversations).
So for me it's never been a question of whether to do it as much as it is how best to do it. It's also not so much whether you're using Creative Commons or some other licensing model; the more important aspect is how is the content being delivered. Some authors are deeply disappointed that they made their entire work available for free and it didn't spur print sales. Oftentimes they'll assume this means the free content model simply doesn't work. I say that's too broad a statement and you need more data points to draw any conclusions. Was it simply a weak product? Was there any buzz surrounding the release? Did anyone even know it was there?
More importantly, when are we going to acknowledge that a 300-page PDF file isn't a lot of fun to read?! Besides the fact that there's no killer e-content device out there (yet), an "iPod for words", if you will, I think we've got to get past the notion that a print-to-online port simply isn't all that exciting, especially if there are no hooks in it to leverage the dynamic e-content delivery platform. It's just like the old joke about the first TV shows: They were nothing more than the same old radio programs, but done in front of a camera.