I play in a community orchestra, and we get people dressed in all types of clothing - usually what I'd call "business casual" (i.e. slacks and shirt/blouse), but we also see our fair share of jeans & sneakers. Things are a bit fancier at the San Francisco Symphony, especially on opening night, but even they get a variety of attire.
Hey, I don't care what you're wearing as long as you silence that darned cell phone! And leave the crying babies at home, unless it's a children's concert.
![Stick Out Tongue](https://pics3.city-data.com/forum/images/smilies/tongue.gif)