Well yes, now you can perform more manipulation of the page without needing a roundtrip to the server, but saving the state of the application still involves one, unless you are the type of radical early adopter who is going to try to do it all with HTML5 local storage.

The relative balance of the work may have changed, but I don't see it as a revolution except in terms of user experience, where AJAX has definitely drastically changed the way users perceive a web page.

Otherwise, the development model of HTTP - the server sends me something, I send a reply, and it sends me back something else - is still alive and well. That's to be expected, since browsers were built with HTTP in mind and the supporting technologies, Javascript included, all must live within that box. The server is still intimately involved with the behavior of the page, but its involvement is encapsulated into individual actions rather than an entire page load (i.e. the server returning an error can be responded to in the context of the HTML form that caused it, rather than with a page redirect or some such). Again, I don't deny that's a helpful thing.