24 March 2013: If you're reading this note, then you've encountered this section while it's undergoing substantial revision; see producingoss.com/v2.html for details.
poss2 tbd: subsections for Twitter, Facebook, any others. Twitter is useful; Facebook appears not to be so relevant to open source projects but check this with people who use it more. Identi.ca (if will persist). Others? Eventbrite (mention from "meeting-in-person" section), what else? Acknowledge that many of these services are not open source; times have changed, the train has left the barn or the horse has left the station or whatever.