To cut to the chase, I am a big fan of this book. I have used it as a reference while coding, while it also clearly explains the topic at a beginner's level.
It starts by explaining how Spring can be used for Inversion of Control and Aspect oriented programming. The code examples used to illustrate the text are short enough to copy and use (although, I would have liked to see links to a web-site which I could have downloaded the examples from - just to save typing effort). The authors include enough details to ensure that the book remains useful as reference material as well as an introductory text - without bogging down the reader who is reading for the first time.
Later chapters cover topics such as integration with other technologies, such as JDBC (or Hibernate or iBatis), transaction control and the Spring MVC (model view controller) framework for the web layer. Although the authors clearly have preferred solutions for object-relational frameworks (Hibernate), presentation layer (Spring MVC) and remoting (RMI), alternatives are given, and their use explained with a fair amount of detail.
I felt that this book was well written, being both easy to understand at an introductory level, and detailed enough to be useful as a reference. The prose style is clear throughout, without skimping on detail.