If I have an IM open in the background and someone sends me a message,
I should get a preview of the message. Aidum and Digsby do this by
showing you the message in a popup window in a the corner of your
screen that disappears after a couple of seconds.
Digsby has taken it an extra step by letting you respond to the
person directly in the preview popup, so I don't even need to switch
screens if it is a quick response.