That's always a popular question when I do this forum. :-)
A lot is new. There's new annotation-driven dependency injection, new Java-based configuration, the Spring Expression language, Spring Security 3.0, Spring's annotation-driven MVC framework, REST support, etc, etc, etc.
Note, however, there are some things that aren't in the book. When I did the first edition of the book, I tried to cover Spring comprehensively...and although I missed a few things, I covered most of it. In the 2nd edition I tried that again and failed miserably...by that time Spring had grown so much that it simply wasn't possible to cover it all in one volume (in fact, entire completed chapters were pulled from the 2nd edition because it would've made the book too big). So, when I approached the 3rd edition, I decided to start over on the table of contents and focus on what I believe the be the main Spring story. So some items, such as Spring Batch, Spring Integration, Spring WS, etc...didn't make it into the book. Those are wonderful topics and I encourage everyone to look into them...but I had to carefully refine the scope of the book or else I'd still end up failing to fit everything in and cutting chapters just before publication.