There was a guy in the coffee shop today with an empty holster (SERPA for a J-frame LOL) on his belt. After I left I asked my gf if she noticed it and she said no. I imagine that if there had been a gun in the holster, no one would have noticed either. Then again, it's a tiny holster for a tiny gun so at a glance it might be mistaken for a cell phone or something.
The only problem with OC is the people who go out of their way to make sure that people notice.
I don't plan to open carry, though I will enjoy knowing that if I accidentally expose the gun somehow I'm not breaking any laws.
I've OCd before in Nevada and in Colorado. I'd say that more than 2/3 of the people I came across never even noticed. Small children often notice, since it's at their eye level.