We do emphasise design patterns in 'Ajax in Action' quite a lot. My experience over the last feww years with what-we-now-call-Ajax is that it can increase the amount of JS in your app considerably, AND increase the longevity of that code, i.e. the same bit of JS could keep your user busy for several hours without a full-page refresh in sight.
Classic web app JS is generally small and short-lived, so it can get away without much design. Trying to write an Ajax app in the same way is a disaster. So, to a JS coder approaching Ajax for the first time, we thought that a good dose of design patterns was`in order.
My original motive for writing the book was to note down all the things I wish I'd known 2-3 years ago, and point out all the traps that I fell into. I knew JS, and I knew design patterns from my Java and C++ work, but it took me a long time to put the two together. Readers of the book will hopefully benefit from my hindsight and enjoy a less bumpy ride!
---<br />Author of...<br />'Ajax in Action' <a href="http://manning.com/crane" target="_blank" rel="nofollow">http://manning.com/crane</a><br />'Prototype & Scriptaculous in Action'<br /><a href="http://manning.com/crane3" target="_blank" rel="nofollow">http://manning.com/crane3</a><br />'Ajax in Practice'<br /><a href="http://manning.com/crane2" target="_blank" rel="nofollow">http://manning.com/crane2</a>