From: Method
What's wrong with using IRC??
IRC is more of a community thing: everyone chats in the same room (yes i know, if you want you can wisper stuff, but that is not the main purpose). in FB the main purpose is one on one conversations. by having these 1 on 1 conversations, it illuminates the mindless trolling that goes on in IRC. and how many times have you heard someone post something positive about IRC on these forums? very few times. Most of the time, i read stuff like "ppl on IRC are jerks".
also having a chat here is more convenient. you don't have to go to a different website or load up a different program.
have a question for another person? well just click on their name and send the message. no more waiting for them to refresh their page in order to see that they got a PM. besides, PMing is like Email. Y Email when you can IM?
that is just my opinion