This is not really an exploit but a neat little trick. If you know someone that is using AIM 5.0, and has a SKIN/Theme enabled, you can make your screenname invsible by selecting a blue backround color for you messages. It also makes timestamps invisible too. I want to give TreyDawg some credit for this because it was his IM, that made me aware of it.
It happens because of skins, im guessing they dont interface properly with the rich textboxs.
-Nemisis