I've taken a training class from this guy before in San Francisco. He's pretty cool but he tries to push his own APIs pretty heavily which I found to be pretty annoying. Other than that it was good.
I was going to post the same thing. It is a great book if you have already some basic knowledge of Javascript but want to really understand the language and how to use it.
I attended a conference and took an all-day workshop from the author of this series. He covered a lot of the content from his books in the workshop, and it was phenomenal. Highly recommended!
The truth is, we all don't really fully know JS, and we all need to work on knowing it better. The books are my way of learning it, and hoping that others can learn along with me. :)