I still recall watching this change firsthand.

When i got my first modem, i was informed of a regional IRC channel on one of the big networks. And from that day onwards i would have my client set to connect to that channel, and fire it up alongside the email client right after the handshake completed.

But at one point the channel died, and the cause of death was twofold.

one part was the creation first generation social media services, and their web based chat rooms.

Another part, and perhaps a bigger part, was that Microsoft made a strong push of MSN Messenger with Windows XP.

This resulted in a more clique style communications form online, as you had to know people and get their account info before being able to contact them. With IRC you joined the channel and that was it.