I bought an "Instant" book from PACKT Publishing once. ONCE. I'll never do it again. Why? In a previous blog post I detailed the lack of, well... anything contained in another PACKT "Instant" publication. These things are like the primer to the primer - the most shallow introduction it is possible to print and still have any ink on the page. It's like books for people that are so scared of technology that they're contemplating leaving the industry, and this book is the last hope to convince them to stick their toe in the water.
Have I purchased or read this book? No. But in the forty-some pages (with big print and lots of screen shots) I don't think one could print enough that I'll ever see value for my hard-earned twenty bucks. Go ahead and try Instant Magento Performance Optimization How-to and if it rocks your eCommerce world let me know. I'll try it, and if I agree I will literally print this book review out and eat it.
Optimizing Magento is a monumental challenge with varied and complex challenges; there is no way this "flyer" by PACKT Publishing can do much more than to validate the concerns with a quick introduction to basic terminology and nomenclature. Save your cash and make with the Google, IMHO.