The current way of navigating between a larger group of Instant Messages is very time consuming and thererby not user friendly.
If many instant message windows are opened, one constantly has to click on the arrow on the left and right to switch between IM conversations. This is not only time consuming, but also makes it hard to see who has already replied to your instant message and who has not, since names gets highlighted if reply has been made. For those persons who are not visible on your window, and can only be seen if the left or right arrows are clicked, it is not visible who has replied and who has not.
It would be an improvement in user friendlyness if the names that do not fit on your window anymore (because you have alot of IMs opened) would be located BELOW the current ones, making them all visible without time consuming arrow-navigation.
I added a picture to visualise the current as well as the improved way of displaying multiple IM messages in the friend window
Maybe the tabs should be vertical? (Just a wild suggestion)