A couple of weeks ago I had the oportunity to review the Pentaho Reporting for Java Developers book, so It reminds me about the cool open source BI platform again.
So far, I've read half of the book and all the insides of this nice reporting tool are very well explained. I haven't used pentaho reporting before but I used Crystal Reports a couple of years ago so I knew the basics of the reporting tool.
When you use reporting tools, the learning curve is slow, so if you can get the insides and details to accomplish not only the basic stuff but things like subreporting, complex styles, etc it would be much better. And I think that's the objective of the book...explain you how to do useful things with reporting.
I'll review the complete book later when I finish reading it.