If it isn't obvious already, I'm deeply interested in the convergence between email, IM, blogs, calendars, contact lists, music playlists, photo collections, etc. It was the original driver for Redfoot and, in fact, drove a lot of my passion for SGML (and then XML) in the mid-nineties.
I've just come across Marc Canter's use of the term "Digital Lifestyle Aggregation". I like it.
I still think RDF or something RDF-like is core: at least the concepts of URIs, out-of-band relationships and relationship types as first class objects.