That's assuming that what's in this book is exceptional (which you can't tell without a preview). I didn't think that Practical Object-Oriented Ruby was incredible, though it is a well-written tutorial of basic OO techniques. You could spend less than $49 on a couple good used copies of OO classics, or many more if you visit the right used bookstore. And it's not even a hard copy so it is competing with the wealth of good free information online about OOP. I might pay $99 for a hard copy of this, but no way I'd pay $49 for a PDF.