Buzz spends a lot of time on the physiology and biology behind caffeine and the effects it has on your body. Caffeinated, however, spends more time on the commercial side. For instance, it covers not just coffee and tea, but the plethora of energy drinks, pick-me-ups, and military applications of caffeine, as well as various food incidents that caused the FDA to take action. For instance, it mentions that the earliest documented source of caffeine was from chocolate, which I thought was interesting, since I'd always thought that the use of Tea in China and India long predated that.
It did provide several pieces of information that I previously didn't know, such as the fact that the orange soda drink, Sunkist, contains caffeine! And a significant amount of it at that! Fanta, by contrast, does not. It never ceases to amaze me what the FDA is or is not allowed to regulate, and the book provides quite a list of kid-enticing snacks that surprised me as containing caffeine.
In any case, the book does explain why in recent years, it's been harder and harder for me to find power-gel or gu type products that don't contain caffeine. It appears to have been used as a performance enhancing drugs by professional athletes ever since it was removed from the prohibited list in 2004!
All in all, I'd say that the book's a quick read and well worth a shot, but I found myself skimming several chapters in boredom as the author never wants to say in a paragraph what he can use an entire chapter to write about. Not really recommended, but as I wrote this review, I realized I learned more from the book than I thought I had, so I can't really dismiss it either.