While short, simple, and providing some useful examples, Thinking in CSS is purely for the very beginner. With this in mind it still skips some of the basics and presumes one knows something about the general format and syntax of CSS or that one will pick it up solely through examples.
Though I breezed through it fairly quickly, it appeared that one or two of the coding examples had issues in places which is more likely to confuse the beginning audience it's geared to serve. (Things like classes and ids that were in the code, but never used.) I wish it had had some more thorough explanation and some more complex examples for everyday or common usages to make it more beneficial to the beginning user.
The overuse of examples which featured Packt Publishing (and seemed to serve more as an advertisement than examples) were somewhat grating after a while.
I'll mention that I got my e-book copy for free on Amazon.