In the "chat" context, I now have two MSN accounts (home and work), a google talk account, an AIM account (which I never use), and an IRC nick on the freenode network. In terms of "social network" sites, which I'll define very broadly, I've got MetaFilter, Flickr, del.icio.us (which I've actually used for work), Facebook, LinkedIn, Last.fm (which has actually been somewhat useful), Blogspot (duh), and most recently Twitter. (Oh, and of course I have home and work email addresses, as well as the obligatory "hotmail" spam-magnet address.)
Facebook might be interesting, but it's clearly designed to pull users into it to see what's going on. Unfortunately, I would find it far more useful to have an RSS feed of my Facebook "News Feed", since I use Google Reader to aggregate my news feeds.
Almost none of these systems interoperate in any useful way. Facebooks claims that it can "import" my blog into the Facebook "notes" stream, which is one less place for people to look, but both Facebook and Twitter provide a status indicator, and there's no clear way for one to feed the other, which might be fun, since twitter acts as a web/IM/SMS gateway and narrowcast channel, allowing me to see what's going on with my "friends" in realtime, and to post what I'm doing easily without having to use a full web browser just to type in six words.
Although it might be argued that Facebook is social and LinkedIn is work, there's enough overlap and cross-fertilization between those two arenas that it would be interesting to see what might happen if they could join forces.
But, for the time being, I'm stuck searching for everybody I know every single time a new site pops up and everybody piles into it. I'm looking forward to the inevitable consolidation in this area.
Well, that or I'll just go back to being antisocial.