While the opinion of others seems to be that this book was a waste of their money, I thought it was well worth it. I've read quite a number of UML books and just about gave up and started reading the spec itself. Then I found this book and thought it was great!
There are clear examples in the front and the reference sections were great in getting my feet wet. If I need more information then I'll read the spec.
This is a great book if you are just trying to get your head around the UML.