A blessing and a curse:
May your website enjoy huge traffic.
A blessing, as all site managers crave a deluge of visitors and buyers.
A curse, because if your site becomes wildly successful, you'll have to learn how to scale your site. When traffic soars, small things that never before caused concern can grow into thorny problems.
I enjoyed the book and would recommend it. It isn't a textbook -- it would be impossible to write a definitive textbook for a topic as far-ranging as site scaling -- but rather reads like a well-organized conversation with Cal.
Most interesting for me was reading Cal's description of Flickr's pain points and how they overcame them. You can feel from his writing how Flickr struggled with Unicode, malformed email from cell phones, mysql scaling, spoofing and XSS attacks, etc.
If you're a retailer running a home-grown e-commerce stack, your engineers will benefit from reading Building Scalable Web Sites.