"Spring Roo in Action" starts out with an example. Similar to the "Rails demo" where you build a complete application in 15 minutes. The book then moves on to how to use the shell and your IDE with Roo. I particularly liked the part about which files are safe to change vs which are Roo only.
The tricky thing with Roo is that readers need to understand a bit about the technologies Roo is generating code for in order to understand the examples. (Spring MVC, JPA, Dojo, Ajax, etc.) The authors cover "the least you need to know to follow." It's more useful as a review than if you've never use the technology. But if you've never used the technology, you wouldn't be generating code for it and expecting to understand it anyway.
The other tricky thing in a book like this is that the authors are experts on Roo (and many other things) but not necessarily everything in the book. For example, the JUnit section mixes junit.framework with org.junit packages (3.8 vs 4.0). And assertTrue(a.size() == b.size()) which gives a less clear assertion failure than assertEquals(a, b). This isn't important but I'd caution against assuming everything you read is a best practice.
However, the Spring and Roo parts of the book are excellent and I couldn't find any anti-patterns in there. In a Roo book, that's what you want to see.
Disclosure: I received a copy of this book from the publisher in exchange for writing this review on behalf of CodeRanch.