This book is quite simply the most useful book on CSS I own, and it's great for several reasons.
Firstly, it addresses real world problems (for example, two-pane layout, three-pane layout, navigation tabs, footers, tabular data, drop-down menus, calendars).
Secondly, there is minimal fluff: the introduction is only 10 pages long (and still contains some technical information), and the first "How do I ...?" starts on page 11; compare this to some books that pad endlessly with pontification about The Bad Old Days of HTML and cross-browser incompatibility.
Thirdly, the recipes are presented in an extremely approachable, standalone format; typically:
1. The question (for example, "How do I create tabbed navigation with CSS");
2. The solution, usually a complete XHTML page (from DOCTYPE to </html>);
3. A screenshot of the result, sometimes in different browsers;
4. A discussion of the technique used.
More complicated recipes will build up the solution bit by bit, showing screenshots of the intermediate solutions to illustrate precisely what problem next needs to be addressed.
Lastly, the author really seems to "get" how important web standards and accessibility are; she exhorts the web designer to test in text-only browsers like Lynx to ensure web sites are accessible to blind and disabled people, and frequently points out Internet Explorer's poor compatibility, and even knows about "minority" browsers like Konqueror.
Compare this to "CSS Web Design For Dummies", which glibly says:
"Some incompatibility issues still exist, but this book deals with them only occasionally ... you need not write complex workaround code to take into account an audience so small that ... many Web pages simply ignore them. [...] History has elected Internet Explorer as the standard ... Just relax and assume that your Web page visitors [are] using IE."