Yes. But every chat application in node.js that has ever been presented in HN faced the same fate of being brought down to a crawling pulp whenever it had more than 100 or so concurrent users.
Popular GUI-clients would be Colloquy on Mac, mIRC on windows and XChat on linux. Just download one and see for yourself; Freenode is a popular network for hackers of all kinds, QuakeNet is the network for gamers (and also happens to be the biggest with ~60k users online at any given time).
IRC is amazing. Servers are linked as leaves to hubs, or as hubs, linking to other hubs or leaves. If the network splits (one server goes down, breaking the tree) it can be quickly relinked to secondary or tertiary servers, restoring connectivity. For its time, and even to this day, it is an impressive protocol that is not only fairly easy to implement from a client perspective, but a very scalable chat server architecture.
More importantly IRC servers have a battle hardened scaling solution baked right in, based on the spanning tree protocol.
Anyone looking to write a scalable chat software would be well advised to study the evolution of IRC. Anyone looking to hack a scalable chat solution would be well advised to use a mature IRCd for the backend.
Citation: http://www.shortnews.com/start.cfm?id=27080
Edit: I hung out on DALnet back when twisted was still linked and when it got taken down the crush of the users, as the article mentions, rendered the network virtuall inaccessible. Goes to show what happens when you rely too much on one link.