For me what is happening with JavaScript and XML is very interesting. The metaphor of the browser back-button is breaking. The central pane of the browser is becoming more versatile.
To some AJAX might be all hype. I have to say that as a language JavaScript isn't much to write home about, and as a platform the web varies from browser to browser. But having been watching web technology now for a good ten years, it really seems like there is a shift going on now. Not everyone agrees I had the opportunity to chat to some that were developing some of this technology the other day, and it surprised me that they disliked the idea of Web2.0, or Web2--- they couldn't put their finger on what amounted to: to them it was hype. They'd always done it. That perhaps is the point, they grew up with it, are part of it and are making Web2.0 a reality.