I've bought this book a few years ago along with the "Oracle Database 10g PL/SQL programming" from Scott Urman, Ron Hardman and Michael Mclaughlin. Comparing these two books, the one from O'Reilly is much more thorough and provides considerably more information about various 'gotchas' and problems related to the topic.
I don't say the other one is not good - I generally do recommend it as an introductory material, and then use the book from O'Reilly for a really thorough study. If you want to buy only one of them, buy this one!