My Hibernate In Action books seems kinda obsolete now since Hiberate 3.2 is available now, and that book is probably for Hibernate 3.0.
In addition, both Spring 2.0 and Hibernate 3.2 comes with very good documentation.
One of the key requirement for any open source projects to be successful is that it should accompany with decent documentation. Just few lets-do-it-together kinda tutorial or "our code is so well written, that you dont need documentation" approach wont work.
I guess buying a book on technical topic is good only if you plan to finish reading it as soon as possible, otherwise newer version of the framework/producet will outdate most of the book. If there is good documentation available, then, we need to be judicious in buying books, because online documentation will be more up to date.