ICQ is a client server app until you open an icq chat. Lets I say I invite 6 people into the chat. 4 people won't be able to see the other 2 and miss out on their parts of conversations. It's very strange. I think ICQ Chat uses peer to peer rather than going through icqs servers. On IRC you connect to a central server, to a room thats permanently there. You can always see the other people in the chat, and you dont have to invite all the people into the chat every time you want to have one.

Sean