This. It was a new idea to me when I started at my current place, now I can't imagine living without it. We've also been through a merger with another similar sized company (with a very different culture, in a substantially different timezone) during my tenure, and evangelising the IRC network was a big thing. The difference in communication efficiency between teams who were quickly convinced that group chat was a positive vs those that weren't was pretty noticeable.
The etiquette thing is important, and varies team by team. Our team has several channels to ourselves with varying levels of formality, and company wide channels similarly (#techteam, title line: "No banter" vs. #companyname, title line: <insert latest in-joke>)
Not only does the group element allow anyone who's taking a quick break to offer some help, it often draws in advice from across the organisation, including people you'd never have thought of asking, who just happen to be dipping in to the channel at the time.
Edit: The office wide "banter" channel's primary purpose most days (so like, not Friday afternoon) is the distribution of fresh coffee, prepared in 5 mug cafetieres, announced and claimed here. So many people have IRC bings on the word "coffee" that it's best discussed in some form of leet substitution if you're not offering to make some.
I've tried, and failed, twice, to introduce IRC into organizations. The first organization wanted policy and procedures around logging all chats - ugh ( yes, I know how to set up logging bots.) At the second, I had most of the team balking on the 'ugliness' of (whatever) IRC client they installed and insisted we use campfire.
I'm more than a little jaded at this point, and would love to hear if anyone has faced and solved these sorts of issues.