I don't want to bore you (and myself) with details of CC-BY-SA 3.0, so if you are interested in the technicalities, I would suggest reading the two threads already linked in the comments:
- Are these eBooks that copy from SE illegal? (Meta.SE)
- Somebody scraped our answers and sold them as a book (Physics Meta)
The main point of contention, from what I can see so far, is the commercial sale of such books. Note, however, that CC-BY-SA explicitly allows this, as long as the work is properly attributed and as long as the derivative work is also licensed in the same way. These latter criteria are debatable (the samples on Google Books do not have hyperlinks to question pages or author profiles), but that seems to be more of an issue with Google rather than with the author, who claims that he has inserted the links in the actual books.
I suspect that it is not only the legality that is of interest to most of the community, but also what action we are going to take, if any. Now, I know nothing about law, but even if this is not 100% legal (due to the incomplete attribution), my opinion is that it is not worth pursuing this in a legal sense. This is for three reasons, in increasing order of relevance:
I have neither the expertise or the patience to read the details of copyright law. It is one thing to talk about ethicality, where my uninformed opinion would count for something, but another thing to talk about legality, where opinions mean nothing. The situation is made even more complex by the fact that the Google Books sample is apparently not representative of the real product.
The author is a longtime contributor on Stack Exchange, has the support of at least one SE employee, and is likely acting in good faith, even if the product is not the... best. Writing a threatening letter (such as that which got sent from Physics.SE) is likely to not be the best way of resolving such issues. I don't blame them for doing it, because they didn't have the knowledge we do now (especially point 3), but we really don't need to go down that route.
If we, as a community, decide that we are not comfortable with our work being published in this manner, then the author has written that he will remove the book from sale and no longer use them in the future. Therefore, if we collectively decide that we do not want this to happen, it is likely that all we really need to do is to inform the author in a nice polite comment somewhere on SE.
To decide what course of action is best, the most pertinent question to ask is therefore not "is this legal", but rather "are we happy with this". To this end I have posted a new meta question and I hope the community will provide some opinions on the topic.