I was reprimanded quite severely (and rudely, I would say) by an usher at the Kennedy Center for taking a picture of my group sitting in the auditorium during an intermission! "Didn't you hear the announcement?" she snarled at me, and when I said "Oh sorry, I thought that meant not to take pictures of the performance", she snarled again "Didn't you hear the announcement? [you blithering idiot, implied]". Seriously, it's outrageous that people who pay good money for tickets are treated in this way.
The Sydney Opera House is also strict about no pix ever.