My state doesn't allow any...yet. That said, I'm an LEO, so I get too, and most of the time not on duty, it's CC, but without worry about printing or anything. I have OC'd off duty a few times, and only once did I ever hear anything. A little girl at a local steakhouse pointed at me and said, in a fairly hushed voice," mommy, he has a gun". The mom smiled at me and told her daughter, " it's alright, he's probably a police officer. I wish your daddy and I could carry ours". I agreed with mommy. Otherwise, as most who OC have mentioned, it's never been really noticed, or mentioned to me.
And the argument about concealment as a tactical advantage is valid, but so is the speed of OC. As far as getting singled out, one can also argue OC is preventative, most criminals I've arrested don't go after hard targets like guard dogs, they go after the sheep. In short, both ways are good, if done right, both have pros and cons, what we need is more folks doing it either way, and doing it responsibly.