Wait for a second printing. The material was solid, but there is a shocking number of typos, errors, misprints, and just plain sloppiness. Much of it I only caught because I'd been exposed to the same concepts elsewhere and recognized poor implementations here -- and I'm not very experienced. For an O'Reilly book especially, this was very disappointing. On the whole, the book was good, but wait for a second printing and a large batch of revisions.