Here's a different resolution  to a problem I've mentioned before: unsolicited email. The typical scenario is that an email goes out to a large group of people and then everyone starts making comments, sometimes completely off the subject. Either way, you may not even care about them. Working in large organizations, the problem can me multiplied because you end up getting on distribution lists that you don't care about at all, but are purely there for political reasons. No matter why you received the email, you don't want to participate in the useless email conversation that seems to be never-ending. If only we could unsubscribe to an email conversation. Basically, it'd be like specifying a conversation as junk email, except there'd have to be some limitations to ensure a separate conversation wouldn't get accidentally marked as junk.