My experience: start a client, join a channel, and watch it go. Meanwhile, try to get work done. I'm either watching IRC in case something interesting goes by (and then not working), or I'm working and then miss whatever was interesting on IRC. Or I try to do both and accomplish neither.
To me, IRC feels exactly like those twitter update widgets that people put on their blogs. I usually end up opening a terminal window and putting it over the widget, otherwise it distracts me like a "look at me!" advertisement.
I get much better value and results from googling; someone has always had whatever problem I'm trying to solve, and if I can't figure it out on my own, I can usually find a thread where someone else has.
I'm not complaining, and I'm not saying IRC has no value (to others). I sometimes wonder if I'm doing it wrong, but I think IRC, among many other things, is just not for me.