I should clarify that I have no problem whatsoever with PA systems. There are very few venues where they aren't necessary (at least, few that I've seen). Besides, my best instrument is Appalachian dulcimer, which is almost completely inaudible if you're more than four feet away from it. I definitely can't gripe about people using PA's. Amplification also takes care of the problem that some instruments are just louder than others, since it can give musicians the opportunity to adjust sound levels.

I hate it when people don't sing along. I'm the only one in my current group with nerve enough to sing anything but I am, quite frankly, not very good at it and I feel a lot like a trained monkey when I'm onstage and the audience just sits and stares at me. I'd rather they didn't talk through our performances but if they don't sing, it looks like they're not having fun or we're not connecting with them. If somebody requests a song and it's within the range of our abilities/style, we do try to learn it for them. We don't care if they aren't great singers (we aren't, either).