I've used IRC a handful of times and the greatest benefit is having instant answers to a problem that may be very specific to my environment. I try not to use IRC unless I'm stuck on something I can't find in SO first. The only times I'll try IRC is when I feel I've tried hard to solve the issue without success. Most of my issues have been solved by SO. I could be missing out on a great way to learn but I feel if I was on IRC I'd be asking too many questions and not digging for the answers myself.