It's happened for us a half dozen or so times, always at lunch. It was a matter of being RIGHT THERE at the podium when they opened. This happened once at Le Cellier, and I asked the hostess what the "trick" was. She said that people often make early reservations, and that they end up not showing up because they're caught somewhere in the parks.
Dunno if that's the rule, but it's worked for us.