So, tomorrow, during 8.30-9.30 PM, the participating world will turn off their lights (and other electrical appliances, perhaps) for Earth Hour. If I'm home at that time, I will turn off the lights and the air conditioner (if the heat isn't devastating, I'll admit) and watch Earth Hour coverage on the news (if any).
I'm not privy to any numbers of power consumption anywhere in the world, but logic says that 1 hour out of 365 days of full power consumption isn't much. It's a statistic. We'd be impressed by the numbers announced by the organizers of how much power was saved during Earth Hour in whatever city, but if we compare it to the total yearly power consumption of said city... it most possibly will be a tiny fraction of it. But still, power conservation is a good thing rather than have no power conservation at all.
But here's why it's important.
Point 1: The only people who will participate (or enforce participation from their surroundings) will be the ones who realize it is important. That power conservation is important, and that somehow, some way, we have to learn to live using energy more efficiently. I dare say we don't turn off everything at the master switch on Earth Hour, but we keep the necessities powered. That's being efficient. Power conservation is not just about using less energy, but it's about using energy efficiently enough so that you don't require too much energy to begin with. Therefore, the more people who participate, the more people who are fully aware of the importance of power conservation.
Point 2: the power of collective sacrifice. Even if we're only switching off the lights for an hour, it's a sacrifice. We're probably sacrificing 1 kilowatt-hour. But if a city of 10 million people switch off lights for 1 hour, we're sacrificing 10 million kilowatt-hours. Sacrificing, for a good cause, at the same time, all together. Imagine what we can do if we sacrifice 1 cent a day collectively to donate to those in need, or sacrifice 1 day out of a week to use public transport instead of a private vehicle to go to work/school. Or perhaps, riding a bike 1 day a week to work/school. Imagine the impact. And when we know what's worth sacrificing for a better world, it will be easier for us to do it together.
If enough people believe that they can make the world better, the world will become better. As long as we act on it - but leave the big gestures to the politicians, and do a small thing first - turn off your lights on Earth Hour tomorrow.