At the Collaborative Technologies Conference in New York City right now, Gordon Quinn, Anoop Gupta, and Melanie Turek are chatting about presence right now. Melanie points out that both application vendors and telephony vendors are coming at presence from different directions, but I tend to disagree with the vendor focus. If presence is truly going to be infrastructure, it needs to be based on open standards so that organizations who deploy presence-based applications are not locked into one provider.
Melanie also says that SIP/SIMPLE is the clear winner in the standards battle. I strongly question that assumption, as you might imagine.
Next topic: real-time communication "dashboards"; do we really think that people are going to use one front-end for voice, IM, web conferencing, calendaring, and all other presence-based applications? Over time I think people have found that special-purpose applications are more productive. IM has traditionally been the entry point for presence, but embedding presence in other applications will probably make more sense than accessing all presence-enabled applications in one interface.
Anoop says that presence is an XML document that aggregates information from multiple entities. Gordon points out that presence is really one aspect of one's real-time identity, which changes moment-to-moment. I prefer to look at presence as a stream rather than a document, but I suppose that's the Jabber way.