To answer number 1, people don't generally care if you hit every note correctly (or know whether you did for that matter). When people come to watch a show, they don't come to critique you. They come to listen to music, relax, get away from life, and just enjoy themselves. If you hit every note incorrect, they will notice and probably won't be able to relax. But for the casual slip-up, most people will still be absorbed in this escape from reality for them that, in the end, they will still applaud and appreciate what you've done that evening.
In other words -- Don't sweat it. Don't even acknowledge that there was a slip-up. It's hard to do, but what the people don't know can't hurt them in this case

As for #2, I've been wondering that myself.