Actually, ICQ uses a direct connection between users to send messages, unless you go to the Preferences dialog and specifically tell it that it should send messages through the server. And, even then, files will still be sent directly. AFAIK, you can not store files on an ICQ server.

Since nobody else could be bothered to list them, here are a few of ICQ's features:

My UIN is 708960, ICYC.