I can't speak for anyone else, but my personal IRC experience has simply gotten more private since the 90's. I still have an IRC client open whenever I'm on my computer, but these days I chat almost exclusively on private IRC channels and servers with people I've known for years. Instead of hordes of people swarming into large, public channels, it's a more intimate -- but just as genuine -- experience.
Still, though, that model seems unsustainable: fewer and fewer people are joining IRC channels or getting into what used to be a "scene." I think there will always be die-hards on IRC, but there's no longer the coolness that there was fifteen years ago.
I have the same experience. I have several group of friends where most people are on IRC 24/7. It makes us even more close to each other to be together all the time like this, and it is just an addition (we do not meet in person less often because of that). I think an important thing to note is that the majority of these friends are not computer scientists, engineers or anything that have to do with computers, but they still learned to use irssi or weechat and screen to join our IRC server :).
I guess the point of my comment is to say that maybe IRC use has changed, but it still is an effective and active communication tool that many people rely on daily, among which some have only known IRC the way I described it: as a communication tool for group of friends (maybe a bit like social networks).
Still, though, that model seems unsustainable: fewer and fewer people are joining IRC channels or getting into what used to be a "scene." I think there will always be die-hards on IRC, but there's no longer the coolness that there was fifteen years ago.