Just a heads up! Chris' awesome All AJAX theme is now updated to version 2.0, featuring a whole slew of improvements:
I posted a little tip on CSS-Tricks the other day about how you can load only parts of other pages on a site via Ajax, and how to do that without needing additional HTML wrapping elements to keep it clean. A common criticism of this is that the Ajax request still loads the entire page, using all that bandwidth, it's just that it only places onto the page the part you specify via CSS selector.
One of the themes that is an exclusive download to all you good-looking people that purchased The Book is the ALL AJAX theme. The idea behind it is that the page never1 reloads. Whenever an "internal" link is clicked, the main content area replaces itself with content that is fetched via Ajax.