Hmm, while I'm all for increasing environmental awareness, I'm not sure that some "symbolic" gesture, at a not particularly appropriate time, is going to be of any positive effect. Honestly, how can any businesses that function at 8:30 pm (and operate past 9:30) afford to turn off or dim lights? (Maybe restaurants, but many of them already have dim lighting!) Also, shouldn't any lights that such businesses have turned on be essential anyway?
And, turning off the lights at well known landmarks--is that even safe? I think the reason that it hasn't caught on in Washington is a very practical one--considering how close National Airport is to the national monuments, one can just see the blaring headlines if a jet crashed into one of them during such time, "Dark times in the city," and such. Oh, the horror.
Now, this symbolism would seem less silly if it were timed better, so as not to try to make people feel as if conserving energy is a type of deprivation. For instance, if Earth Hour was on Valentine's Day instead, folks would be willing to keep the lights out all night that night! (However, having the stereo on to hear the following music to swoon by would be considered essential electrical use!)