I would like to be able to create tags and associate people with those tags, so that I can just tag a link and it will automatically be sent to those people, on

I would like to be able to create tags and associate people with those tags, so that I can just tag a link and it will automatically be sent to those people, only if they have not already seen the link -- otherwise add me to their conversation so I can read what have already been written about it. That way we won't have to disturb each other for being late to the party.