Even though I've already worked with Vim in my day-to-day business I bought this book and what can I say? Well it teached me many new things and it made me become a lot more productive than I was before. If you really want to know about the gritty nitty stuff Vi and Vim have to offer you should buy this book.
It is well structured and covers the most important topics in a very senseable approach. Besides that it also has a part about other Vi clones such as Elvis, so it really comes as a complete book about everything you ever wanted to know. It starts with an easy introduction, offers some small typing exercises just in case you dont have some practical example yourself.