We generally see quiet, sit-down shows where you could easily hear a pin drop. Audiences are generally very respectful and attentive. How do you shoot in those situations?
If that is true, you don't. Shoot that is. There's nothing that pisses me off more than some dumb@ss (not saying that's you, just saying) that disrupts the show by slapping their mirror or just generally brings attention to themselves via the act of photography. And I say that as someone who loves to make photographs of jazz and at times classical/chamber music.
Depending on the situation and type of music and specific piece, the best thing you can do is wait until the absolute loudest part of music, the climax of a piece if you will, and only snap off a frame at a time during those moments. If you are talking about chamber music, you should be very careful, because again, you DO NOT want to be THAT guy. Or maybe I should say, PLEASE don't be that guy -- people did not come to a show like this to be distracted by you. The truth is, for classical/chamber music, most venues do not allow photography during the performance, and when they need professional photography, it is arranged beforehand and done during dress rehearsal, not during actual performances for these very reasons. This is why you pretty much NEVER ever see any photography happening at national/world-class symphonies, not by pros, not by anyone. Beyond dress rehearsals, the few exceptions might be outdoor venues.
It is true that some SLRs have "silent modes," typically the ones that have live view shooting. However, that only minimizes the number of mirror slaps/cycles, you'll still get a least one in there no matter what, plus at that point, you've basically lost what little autofocus you had in low light, you're holding the camera in an awkward way that's more likely to produce shake, and you also now have your LCD blasting away, which is annoying to others in and of itself (I generally disable review completely in these situations, so no LCD at all).
One other comment worth mentioning beyond the point-n-shoot, which will probably just produce crap anyway, is a good old fashioned film rangefinder. Most people have completely forgotten about those puppies, if they even knew what one was in the first place, but slap in some 1600-3200 speed film and you can make some decent shots -- and depending on the rangefinder, some of them are nearly silent (there's no mirror, heh), and because it's 35mm film, you're essentially getting as good if not better resolution than your digi rebel.
And one final comment from someone who has been in this exact situation many times, don't forget that even if it's impossible to not disturb the musicians and audience during the performance, you can sometimes make great candid shots during applause. It might not be a "performance" shot, but I've made plenty of really great photographs of the musicians smiling and soaking in the appreciation of the audience during those moments of applause (and it's so loud at that point, you can just fire a stream of shots no problem). And most audience members won't notice in those moments, or if they do, will nonetheless appreciate the fact that you waited until then to shoot.
Anyway, that's one man's opinion/experience. Good luck!
BTW, here's a
good example of photos from dress rehearsal, audio from the actual show, heh... (There's actually a shot or two from behind the soundproof glass of the soundbooth during the performance. And if you're wondering about the audio source of that show, it was made with only a meter split omni pair of AKG482s DFC 9' high in the sweet spot running into an R44 at 24/44.1.)