This book focuses on the persistence framework of EJB3: JPA. It offers an excellent treatment of this subject. It is detailed and clear.
That being said, it is not a complete treatment of EJB3. For that I like the O'Reilly book by one of the JBoss leads.
Enterprise JavaBeans 3.0
Paperback: 760 pages
Publisher: O'Reilly Media, Inc.; 5 edition (May 16, 2006)
Language: English
ISBN-10: 059600978X
ISBN-13: 978-0596009786
The O'Reilly book and this Apress book complement each other.