...the way web design is changing. Everyone knows nested tables are old-school, clean semantic (-ish) XHTML is newschool. On top of that, ECMAScript is finally being used as it should be in places like GMail etc. etc, leading us to decent webapps that actually take advantage of 6-series functionality (I would argue that Gecko, Opera 7 and Safari will go "7-series", i.e. next generation, if they ever adopt some of the specs that WHATWG is working on.)
However, in terms of UI interactivity and dynamicism, HTTP and SOAP can only take us so far - as far as client-server can take us, after which we need to look to P2P. This is where you're left with the choices of ActiveX or Flash. XMPP is my attempt at a third way, by providing a network layer in which we can do (e.g.) multicast, and all the other stuff that the JEPs offer us.
XMPP and DOM together can offer us a lot more than just a chat sidebar. It can do RSS [as PubSub shows, see comment], VP like Lluna, etc. etc.
However, a dangerous side-effect of giving a DOM full XMPP capabilities could be spam and self-replicating documents. This is something I'm working on. Until I have a 100% bullet- and spam-proof solution my solution is "don't do it". I think that most solutions seen so far, especially those revolving around code-signing, are completely broken, purely because they don't express exactly what TRUST means in this context. Would you trust a company called "click here for your free calendar"? Neither would I, and what this means is that the interface is broken and users are being mislead.
Enjoy your weekends.