How does the HN community use IRC? Any tips on how to successfully use IRC to promote a company, product or project?
I'd say most of its interest comes from the support channels like #rubyonrails or #python where you basically help people. After a while, you get to know regular users and thus making new connections or even friendships. As an example, I've got friends hanging out in a french sys-admin related channel who sent to me people looking for python training. I made an offer and we later called to them to finalize the order. I'd say such things are a consequence of your genuine participation in channels rather an objective in itself.
I use quassel as an IRC client, the core is installed on my personal server, being always connected. I connect from my home or my laptop and always get only what I haven't read thanks to quassel acting a bit like IMAP. I also have a bitlbee setuped in order to act as a gateway to gtalk and hipchat, meaning I got every single possible chat protocol I may use in quassel.
I desactivated notifications, which means If I minimize quassel, I won't see anything, letting me focused. After each focused work cycle ( like every 30-45 minutes ) I just check if anything happened there and answers depending its importance and my current priorities. I don't say I'm not available, which may lead in a debate on why I can't answer right know, I just don't answer back until I got prioritized stuff done first.
This way I can handle chat with wrecking daily productivity. As opposed to that, phone just trouble my productivity, I almost never answer on my phone except for a few people and use almost exclusively chat to avoid that.
You're not going to be able to use it to market a product, unless you're specifically targeting hackers or bearded system administrators.