At this point there really isn't much of a debate; using Google's CDN to load jQuery isn't likely to benefit the majority of your first-time visitors. You're almost certainly better off bundling jQuery up with the rest of your site's JavaScript and making sure you're serving long-lived cache-controlling headers with it.

pjax is a jQuery library that takes regular old page navigation links and turns them into triggers for fast and unobtrusive ajax content loading. Thanks to modern browser features, page URLs, titles and browser history are all updated as usual, even though the pages are not actually reloaded. Like magic!
pjax takes advantage of a recent addition to the browser toolbox: the HTML5 History API. This API allows a JavaScript driven web application to push paths into the browsing history, making it possible for the user to use the back and forward buttons on dynamic content changes, just like with regular page loads. Take a look at the pjax demo to get a quick idea of how it works!

Before the History API, the only way to keep history state and provide permalinks for dynamically loaded content was by using a hack that involved URL fragments, which is a common technique that has recieved some criticism recently.

No images, no external CSS
No dependencies
Highly configurable
Resolution independent
Works in all major browsers, including IE6
Smaller than an animated GIF (3K minified, 1.7K gzipped)
MIT License

Lifehacker, along with every other Gawker property, experienced a lengthy site-outage on Monday over a misbehaving piece of JavaScript. Gawker sites were reduced to being an empty homepage layout with zero content, functionality, ads, or even legal disclaimer wording. Every visitor coming through via Google bounced right back out, because all the content was missing.

JavaScript dependent URLs

Gawker, like Twitter before it, built their new site to be totally dependent on JavaScript, even down to the page URLs. The JavaScript failed to load, so no content appeared, and every URL on the page was broken. In terms of site brittleness, Gawker’s new implementation got turned up to 11.

Every URL on Lifehacker is now looks like this http://lifehacker.com/#!5753509/hello-world-this-is-the-new-lifehacker. Before Monday the URL was almost the same, but without the #!. So what?

You should take time to design your URL structure. If there’s one thing I hope you remember after reading this article it’s to take time to design your URL structure. Don’t leave it up to your framework. Don’t leave it up to chance. Think about it and craft an experience.

URL Design is a complex subject. I can’t say there are any “right” solutions — it’s much like the rest of design. There’s good URL design, there’s bad URL design, and there’s everything in between — it’s subjective.

But that doesn’t mean there aren’t best practices for creating great URLs. I hope to impress upon you some best practices in URL design I’ve learned over the years and explain why I think new HTML5 javascript history APIs are so exciting to work with.

moo.fx är ett litet enkelt javascriptbibliotek för att storleksförändra objekt och andra javascript-effekter.

Behaviour är ett bibliotek för AJAX-funktioner som verkar rätt populärt och bra.

En samling snurrande ikoner och "progress bars" för att användas (fritt) på webbsidor.

Artikel om hur säkerhetsproblem när man tillåter stil och anpassning i koden.

Ett "framework" för att smidigt använda javascript för Ajax-funktioner.

HTML_AJAX är ett PEAR package för att göra AJAX-operationer för PHP

Aaron Swartz förklarar historien bakom begreppen "AJAX".

SACK - Simple Ajax Code Kit - är kod som gör det enkelt att använda Ajax i webbapplikationer och som ska vara säkrare än saker som SAJAX.

Hur man jobbar med användarvänlighet (usability) för XMLHttpRequest i praktiken.

En toolkit för att använda Ajax (XMLHttpRequest mm) från PHP.

En artikel hos XML.com om hur man använder XMLHttpRequest, men förklaringar och exempel.

En dissektion av Google Maps som använder avancerad webbteknik för att leverera sitt resultat.