I think the line tends to fall between the programmer types and those of us with less of a comp-sci background on this book. I stepped up to this from Jeremy Keith's DOM Scripting after a wild self-teaching binge and enjoyed reading it. It's considerably less dry than you would expect from a book of its size and I thought the author did a good job of explaining more complex JS topics. That said, some topics were starting to show their age and it's overdue for a new edition.
Overall it's a great introduction to people who want to pick up tricks across the entire gamut of JS and I found myself running into a number of objects and methods I wasn't very familiar with. When I'm looking for new JS ideas I would go to this one and start browsing sections I hadn't read as thoroughly. When I want to know exactly what is up with a given facet of JS, I go to O'Reilly's version, the Definitive Guide.
My copy was from the library unfortunately and I miss it, but I'm still holding out for a third edition as it's getting a bit long in the tooth in some sections, but this is usually obvious (like pre-ajax coverage of the XMLHTTPRequest object).
There is definitely room for both the definitive guide and this JS book on my bookshelf, however, and I personally thought it did a great job on prototypical inheritance for doing OOP-style JS.