Currently if showing of previous conversations is turned on one can be confused when old chats are shown close to the current. Also the date shown above adds to the confusion. E.g.
Tueasday, November 30, 2009
friend: hi, how are you
(current message) friend: hey? where have you gone???
November 30 looks like the date for all those messages. So, it could be a black or grayed out line dividing old messages and the current conversation.