A truly great and ground-breaking book. It was as much a pleasure to read again in 2012 as it was the first time I encountered it 25 years ago. Its analysis and advice are at least as relevant now as they were at the original publication date. (A few examples from the "computer era" are visually dated, but you can see slicker versions of the same problems and errors all over the web and on mobile device apps.)
For those who don't know the book, it is an analysis of what makes a truly great presentation of quantitative information work -- where the meaning of "truly great" includes easy to examine, easy to understand, multi-levelled (you can get information at various levels of detail just by how you look at it), accurate and informative (not misleading), visually beautiful, parsimonious, and inviting or intriguing. It invites and challenges the reader to think about how data presentation can be designed for the user to get the most out of it with the least cognitive load, misunderstanding, and distraction, and the maximum of delight and engagement.
The design and presentation of the book exemplifies its message, with diagrams and examples integrated with the text so that each reinforces the other, and a graceful and helpful use of typography and text layout to bring out the important messages. Tufte is an engaging and personal writer, and he is direct about what he likes and doesn't like and why. Because he is insightful, brilliant, and witty, his prose style too is part of the book's appeal.
An essential on the shelf of anyone concerned with communicating complex information visually, including people like me who design software user interfaces.