In Wildfire2.6, we've introduced support for the Publish-Subscribe extension to XMPP (Jabber). A loose analogy is that it's like RSS on steroids, but for instant messaging. A slightly more technical take: it's a comprehensive system for publishing and consuming topic-based events.
Like RSS, pubsub offers a simple way to get notifications. But far beyond RSS, pubsub has rich publishing and permissions systems. As a more radical example than standard news syndication, a company could use pubsub to power a file sharing service; certain users would be allowed to publish files, while others could read them (with optional moderation). Users would be notified in real-time when files are added or modified, and could even filter notifications using keywords. Other IM twists to the pubsub protocol allow you to choose to only receive events when you're online, use your buddy list for permissions management, etc. The reason we're excited about pubsub is two-fold:
It's much more comprehensive than the existing mainstream event protocols like RSS and Atom, which means you can do much cooler stuff. Of course, RSS and Atom should be thought of as complementary rather than competing technologies since they're for a different medium.
If you believe like Jive and Google that an XMPP instant messaging client will be on every user's desktop, that means pubsub is a viable<span style="font-weight: bold"># platform</span># for building all sorts of services.
At this point, pubsub is just an interesting technology that remains to be proven. However, we'll be building some innovative services on top of it and I'm sure others will be too.
If you're interested in learning more about pubsub and how it can be applied, read our article on the topic.