I found this great because it gave me a way to think about something familiar in a different way. I’m use to thinking about XMPP as just an IM and presence protocol, used by applications that let humans to communicate with other humans. But I didn’t take it one step further and think of it as a messaging service between machines, mostly because I was under the impression that polling problem was solved (by the likes of Comet).
That way we should be able to build browser apps that need near-real-time updates. The obvious one is chat. In fact, most of our XMPP clients are specialized to do that. Other applications are collaboration software, like a shared whiteboard (if sending SVG over XMPP would not be a bandwidth hog). Video lectures with auto advancing slides might be another one. Fleet tracking might be another. MMORPGs would also be easier to write on such a platform. It’d be interesting to see where this goes.
Update: Looks like people already tacked XMPP onto Mozilla