Betcha noticed this today. Good for Google; let's see if we notice lights out between 8 and 9 p.m. tonight.
I somewhat suspect that life will go on fairly normally between 8 and 9 p.m. And granted "Earth Hour" is mainly symbolic. But in an ironic sense, the lack of being able to discern much change in lifestyle during Earth Hour is the most apt symbolism.
AP says lights are noticeable dimmer in Sydney. Take a poll on whether you plan to participate.