According to a contact in Australia, during this year's Earth Hour 'the saving was equivalent to two power stations being temporarily out of service.'
Last year it was a Sydney-based event. This year it has gone global. According to the BBC link in the previous post, (which keeps changing some of the details) Chicago and San Francisco took part, along with Bangkok, Manila, Toronto and Dublin. New Zealand joined in as well. In Bangkok they saved 73.34 megawatts of electricity, which would have produced 45.8 tonnes of carbon dioxide.
In Britain, a number of villages arranged their own lights-out, although there has been no big publicity. 26 councils dimmed lights. I don't know which they were. On the south coast, Brighton turned off the lights on its pier, and in London - which was not officially involved - lights were turned down at City Hall.
Next year, will there be more? I guess it's our call.