This book repeatedly makes it clear that it's aimed at pedants like me who find the rules of English grammar and punctuation interesting, even if we don't necessarily get them right all the time. It's a conversational guide to the use of (mostly British) English punctuation, with lots of examples, anecdotes and quotations; it includes a section on each of the common English punctuation marks, along with some general rants.
The author's writing style is clear and entertaining, and I can't easily fault the book on its content; it's probably not a good book to read anywhere where you'll get odd looks if you occasionally burst out laughing for no apparent reason. It's nice to see the author mentioning halfbakery as a source of bizarre ideas.
Typographically, it's a somewhat odd-looking book: it's set with narrow paragraphs and huge margins, causing huge variations in inter-word spacing, and the italic face used (FF Quadraat?) is condensed. It's not unreadable, just irritating. I'd also take issue with the author using "the internet" and "CD-rom"; pedantry comes in many flavours.
I'd strongly recommend it as a couple of evenings' entertainment for those of even moderate pedanticism.