For the moment, lets ignore the fact that ant comes with a comprehensive manual.The book gives a nice overview and motivation for ant, as well as a sample project which will help you get up to speed quickly. There is a comprehensive chapter on data types and a nice example of how to build your own task.
I was happy to see that OReilly editing quality remains high which sets it apart from other publishers.
The only complaint I had when I first read the book is that I thought that the codes given to the various task parameters in the task reference were a bit cryptic. The book also mentioned that ant 2.0 was due out in 2002, but here it is 2004 and I only see 1.6. The book also provides installation directions, which should really be an appendix since most folks probably just install the RPM or .deb these days.
But ant does come with an excellent manual, which is up-to-date.
It does appear that the book is not too much more than a cover for this documentation. Unlike the book, the task reference in the bundled manual organizes the tasks by function, which is useful. The list of parameters for each task is better organized: it is in a table, it eschews the ant version for the parameter, and there is a Required column (instead of a cryptic code as in the book).
Id recommend that you borrow or read this book on safari.oreilly.com for a nice introduction and then use the bundled manual for more examples and a reference.