A friend of mine worked as stage crew on stage on the lake over summer 2007. The crew was virtually flipping, when they were told, that that they wanted to shot a scene of the new Bond movie on the Tosca stage and a bunch of my friends auditioned as opera audience. Unfortunately non of them is visible in the movie, but my stage crew friend was sitting in the cinema all excited, exclaiming "look, look I cleaned up the rail where he's standing! Oh and there I cleaned too" every 20 seconds. :)
What was fun too, was that the scene starts with a plane landing on Bregenz airport, though the real Bregenz doesn't have an airport at all. Then they are driving through the old town to the Tosca performance, only that it's actually the old town of Feldkirch, a town nearby.
And then during the Tosca performance everyone is wearing light evening gowns. This was shot in early spring, so the people must have been freezing. I've seen Tosca in August and it was chilly even then out there on the lake, usually everyone there is dressed in very warm clothing and seasoned opera fans are bringing blankets (save for the people in the VIP lounge)