In terms of quality, I'd rate this book as high as anything from Glasshaus, most prominently "Cascading Style Sheets: Separating Content from Presentation".
This book covers a lot of the same ground as the Glasshaus title but I found it particularly useful due to its slightly more graphic design bent. The code samples in the book are not merely basic utility layouts (2 columns, 3 columns, vertical centering etc), but more aesthetically 'designed' examples of using CSS -- a feature clearly missing in a lot of books aimed at the 'web developer' community. I'd venture to say I am not one of those to get so enamoured with the technology itself that they fail to see it as a handy means to an end. I really value Schmitt's efforts in this sense.
There are many CSS techniques in the W3C specifications that are poorly, inconsistently, or not supported at all, in even the latest browsers. As a practising designer, and not just an academic, Christopher is only too happy to point out the limitations of browsers and explains some of the many pitfalls that await the unwary if you try to push the envelope too far.
The projects, again downloadable from the publisher's Web site, focus on publishing - in business, personal and 'underground' styles. The typography is a lot fancier than any other book I've seen and the attention to detail, even for 'web' typography, is highly commendable.
An earlier review on this website said this book is not well technically edited. I am not sure why that was said, but I work with Opera 6 (and 7 beta), Mozilla 0.9 and above, netscape 6 and above and IE 4 and above. All samples I have tried have impressed me.
In sum, if you want to separate your content from design and give your 'styles' some, er, style, AND if you are fairly familiar with the basic CSS lingo (i.e., you dont need to know box models or glish but should understand what a link rel is), then this is probably a very useful book for you. If you are looking for a very basic introduction to CSS, I'd strongly recommend the Glasshaus book. If you are serious about your work, get both.