I've previously mentioned the explosion of interest in adding real-time features to social networking applications using XMPP technologies. The list of services that are deploying or even just exploring this combination of technologies reads like a who's who in the space: Twitter, Facebook, Mozilla's Songza and Bloxes and Weave, Yahoo's Fire Eagle, Dopplr, Jaiku, Seesmic, Sharpcast, Threadless, NewBay, Spotify, Gnip, OpenSpime, and many others (including some big ones that have not yet "decloaked").
If you're interested in XMPP and social networking, there are two upcoming events you might want to check out:
If you can't make it to either of these events, don't despair: we also have a dedicated mailing list at social@xmpp.org for ongoing discussion of XMPP and social networking. They're two great tastes that taste great together! :)