Any technical book in print is out of date before the ink/toner dries. Jeff's book was written when 3.0 was basically in late beta. He mentions quite a bit about 3.0. I would say that most of the details still apply, but it does lack details on the recent changes.
Also, Jeff has been keeping the example code from the book updated for the latest version of Alfresco. He regularly posts those updates on his website.
On the whole, I'd say the book is still worth the money, but I am anxious for the next edition.