The live pitch correction kit used to be really expensive, but folks like DBX and TC Helicon now make very sophisticated gear that is well within the reach of the 'Weekend Warrior' musician. People are using it, and it's becoming less noticeable as the electronics improve. That said, it's worth listening to the various 'singing contest' shows on TV to get an idea of what's going on. On the 'live' later stages of these shows, pretty much every performance is pitch-corrected, and quite heavily at that. Sometime the singers are so far out that the software chooses the wrong note.