I'am 18 and I agree with you. The way the discussion one day happened in status updates have now moved to usually hidden groups. The groups are usually built around some specific event, say prams, or alternatively around some common interest such as LAN gaming or binge drinking. It works as a new and more appealing way to create what you may consider mailing lists. Engaging in those groups is easier as you post something relevant to the topic and know that your or your friends aunt will not see what you said.
I think boomzilla was talking about electronic bulletin boards, i.e. BBSes and the web-based forum replacements that grew from them. (And it's an apt comparison -- forums remain an important social aspect of the web.)
