Well, maybe it could be another opt out feature because some of us do use it. Sometimes I need to know if the person has received the message or not (not all messages require responses but still need acknowledgment). Some messages I've sent have taken several days for the other person to get around reading. I would have wondered about the silences had I not known that they had not yet read the message. If too much time goes by, then I know that I should try to rach them in another way. Maybe because I don't read or send many IM messages, I still find it a convenience to have that notification.