I can't try it out at the moment... but heres what I meant:
Contact1 sends you a Message (window minimzed and window pops up when Contact1 starts typing a Message to you)
You look at Contact1's Message, begin to Reply and all of a sudden, Contact2 starts typing a Message to you & now you are typeing in Contact2's Conversation window.
(Perhaps sending the wrong Message to the wrong Contact If you aren't paying much Attention)
So if you fixed that, thats good
Edit: Perhaps keep the window focused on the Latest Contact that types you a Message and makes the Window come to the front, and let the User switch between tabs as he/she pleases. And the next time a new Message is sent while the Conversation Window is out of Focus... Bring the Window to the front with the latest Contact that has started sending you a Message.
* I'm mostly thinking of people using Tabbed Chats here... I know alot of people use Tabs
