It is a noble concept and a demonstratable one too as was evident from last year. The newspapers reported a significant reduction in the demand profile for that one hour period. So, yes, it is a workable concept.
However, I was not part of the event last time around. Nor am I going to be part of it this time or anytime in the future.
I feel problems like global warming should be attacked by long term sustained continuous methods - such as judicious use of electricity, using public transport to the maximum etc. One time radical actions do not achieve much. Did the people use electricity judiciously after the previous campaign? I don't think so.
As a part of the set of people working in the electricity sector, I find on the other hand that demand has shot up, costly power needs to be purchased with ever increasing regularity and the amount of renewable energy expected on the grid is not reaching the required levels.
I believe instead of an annual Earth Hour, we should have a "life-long earth lifetime". It will be so much more effective.
On the flip side, I am aware of the "spirit of activism" and the legendary inertia of the human race to inculcate good habits such as consistent electricity saving. In this regard, this is a good move, and I wish it all the very best.