You're asking on Hacker News if people still use IRC? In this same discussion thread where people are talking about writing Gopher clients?
Yes, it's still in very wide use. The numbers might be declining as greybeards retire and noobs pick Slack instead, but there's still plenty of us out here.
It's the default method for technical channels such as programming or OS projects. Please, use IRC with TLS if you can.
Also, Usenet is still good for Slackware and C users, you'll have a high level there. comp.lang.c.moderated and alt.os.linux.slackware are really good. Also, the ones for Interactive Fiction and Nethack, I can't remember the groups. rec.games.roguelike.nethack, maybe.
Yes, some communities are still huge (Freenode).
Freenode is where I turn when I'm completely stumped by a tough problem. Some helpful person usually points me in the right way quickly. Sometimes I can even point someone in the right direction myself.
Freenode is actually growing I’ve heard.
yeah, it's the last bastion against Eternal September.