> The point is that with AIM (or instant messenger, generally), you knew who was up for chatting. If someone wasn't up for chatting, they either would have an away message or wouldn't be signed on at all.

That's an interesting feature I think, but nothing is preventing that to be implemented on a new or current chat program. It would solve the distraction problem of always being available and online.

I made quite a few friends as a result of friends-of-friends joining a chat, friend leaves for the night and the conversation continues even without the intermediary friend. That happens with IRL interactions sometimes too but not as often in my experience, usually everyone leaves if the links are broken. I don't think most people would continue a conversation with someone they didn't really know after they happened to be part of the same group text either.