This time last year, I described Earth Hour as "a largely meaningless piece of slacktivism where people pretend that one hour of environmental posing by switching off lights is more important than long-term behavioural change". That's still what I think, and the folks behind Earth Hour are obviously alive to that kind of criticism, since the theme for this year's event on Saturday is "go beyond the hour", encouraging people to make long-term changes.
That's a worthwhile goal, and I'm all for people making more permanent alterations to their power usage and other habits (our post last year offered some thoughts in that regard to get you started). But I'm not going to go out of my way to switch off lights and other appliances on Saturday night, precisely because I do that kind of thing on a regular basis, and I think symbolic gestures are largely a distraction from the bigger issue.
That said, I don't imagine everyone will be emulating my curmudgeonly ways. If you're doing something unusual and interesting for Earth Hour, tell us about it in the comments.