Chapter 3 was really interesting as it covered jQuery and how to create a really good script within your theme that will rotate through sticky posts using jQuery's fade functions. The first half of the chapter looks into what jQuery is, how it works and what is does. The second half is a case study of the "rotating sticky node teasers" script, and how to add this to your theme. The case study looks at each function one by one, then the major parts within that function making it easy to read and easy to understand.
Chapter 4: Drupal Behaviors looks into the Drupal.js library, another two case study is also included in this chapter explaining the use of Drupal Behaviors with jQuery. The first explains the creation of collapsing blocks and the second explains the creation of a simple text editor.
The buzz words around the internet in the last few years has been AJAX, Web Services and APIs, these are all covered by Chapter 7: AJAX and Drupal Web Services. Two case studies are used to help explain this a real world situation. Web clips with RSS and AJAX and Real-tim comment notification are two great little projects that many sites could make use of.