It could be because I am old, but I really like IRC for a casual discussion about a topic. Forums and mailing lists are great for more formal questions and replies, but IRC tends to lend itself to more friendlier (in most cases) discussions of things that doesn’t require the same level of seriousness.
I don’t mean this that IRC is just a social thing, but I can ask about something (perhaps an unexpected behavior in the OS) without having research the item first. A general “Anyone ever had X do Y before” question with a simple “yes, but upgrading fixed it” is a useful conversation without having to get all of details that are needed for a userful forum post. Also, it can be a great place to learn new things to do with your OS as you chat with others and find out what they do with the OS.
Now at the same time, there are some questions that aren’t easily discussed via IRC and in those cases the forum is still the better option.
I am hanging out in #netrunner and #netrunner-os on Freenode and plan to stay here unless someone tells me of another channel/network. I go by technoidX or technoid_ usually, so say howdy.
*someone was already in #netrunner but not sure if they are there about the OS or the card game. Don’t want to take over their channel if they are there about the card game, so also joined #netrunner-os.