Locality, interesting. I'd agree on BBS'. My experience of IRC, thought on efnet was expanding past my local calling area.
IM definitely took the bite out of IRC because it was far better at creating beginners that never made it to IRC, and a lot of IRC users got pulled to IM. ICQ, Yahoo, AIM, MSN created a new type of connection.
The best private conversations start by branching away from a public space. It's that juxtaposition that makes each half all the more special (think noisy club/bar vs outside). I think the biggest failing of IM is that it's easy to end up with a declining circle of people whom you communicate with. Without a public space to replenish ideas from, privacy becomes a curse. IRC allows both.
