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I usually leave iChat open through the night, but when I woke up I had the disconnect message... just thought it was my connection.

In my IM experience, I have had a near-perfect experience with AIM... but when I used MSN I experienced daily disconnections, while my AIM stayed open and fine. that was 2 years ago, might be different now but from what I have heard, its the same
 
My iChat connection to AIM was dropped, too, but the network problems got worse. After several unsuccessful attempts to get back on iChat, the Mozilla download I was running stopped. I assumed that OS X needed a reboot, but after OS X again couldn't find a network connection, my "Aauggh" joined the other "screaming teenagers" who had been disconnected from AIM. My router had gone down, disabling all the network connections in the workgroup. I had to power down the network and bring the router and modem back up separately and manually.
 
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