Article on Ars Technica that points to recent surveys that show teen email use is down, and technologies like IM are more in vogue at the moment (see Teens: E-mail is for old people).
User Friendly responds to this here and raises a good point about the nature of interactivity. If you want responsive and real-time communication, why not incarnate?
BTW – I started using email in 1987. That must make me really old.