It's hard to overstate the value I've gotten out of Freenode IRC over the years. The #postgresql channel is chock-full of contributors and PG gurus willing to generously spend time explaining concepts and best practices. A real gem. Same thing with #clojure and #haskell . ##networking is great as well. Pretty amazing to drop into the same channel for 6-7 years in a row and see the same faces every time.
One of the first things I used to teach devs on our team was how to ask questions on IRC to get the answers they were looking for. When you're working with niche tooling, building personal connections and relying on the community becomes irreplaceable.
Wish people IRCed mode, wonder what the trend with that has been recently with Slack taking over.