My reaction to spidering hacks is somewhat mixed. On one hand, it introduced me to some cool ideas and resources that I wasn't previously aware of. On the other hand, it's limitations and approach were sometimes frustrating.
O'Reilly's Hacks format involves each section of the book being presented as a mostly stand alone Hack that shows you how to do a single interesting thing. If you are looking to quickly learn how to do any one thing covered by a hack, this is great. It takes away from the book as a complete package though. Some topics the book covers, such as An introduction to LWP, don't really fit as a Hack, but that is how they are presented. Almost all the code in the book is written in Perl, but there are hacks that use Python, PHP, and Java. These seem very out of place as the book devotes no more than a singe hack to each of these languages. In some hacks, the Google or Amazon APIs are used, but very little context is given for them, possibly because O'Reilly doesn't want too much redundant information between this book and their Google and Amazon Hacks books. Additionally, because the hacks are meant to be somewhat standalone, and are often contributed by different authors, a lot of very basic information tends to be repeated from hack to hack, anyway.
Ultimately I think the book is a good intro to the interesting things that can be done with spidering and screen scraping. A prior knowledge of Perl and some patience for the Hacks format will help the reader get the most from it. An additional plus is that even experienced spider writers will probably find some cool tidbit they weren't aware of scattered amongst the Hacks of this book.