"On 31 March 2007, 2.2 million people and 2100 Sydney businesses turned off their lights for one hour - Earth Hour. If the greenhouse reduction achieved in the Sydney CBD during Earth Hour was sustained for a year, it would be equivalent to taking 48,616 cars off the road for a year." - http://www10.earthhourus.org/
On Saturday, March 29, 2008, Earth Hour invites people around the world to turn off their lights for one hour – from 8:00pm to 9:00pm in their local time zone. On this day, cities around the world, including Copenhagen, Chicago, Melbourne, Dubai, and Tel Aviv, will hold events to acknowledge their commitment to energy conservation.
As for large aquariums....
The Monterey Bay Aquarium will joined thousands of other businesses that have committed to observe "Earth Hour" on Saturday. The aquarium will shut down non-essential systems between 8 and 9 p.m. Saturday and asking employees to shut down computer work stations, turn off lights in empty work areas and turn off non-essential electrical equipment during the weekend. The Earth Hour program was developed in Sydney, Australia, last year to dramatize the need to address global climate change.