If London takes tonight's (Sat 27 March) Earth Hour as seriously as some of these cities then the difference could be quite noticeable:
http://news.bbc.co.uk/1/hi/world/8590756.stm
You mean there'll be grey clouds instead of orange :o
Hmm - there's some cheating going on here.
Take the Sydney "dark" image and brighten it up - it looks almost exactly like the "light" one. Its difficult to find any light that was switched off between the two.
Mark,
They must have realised it was a fake, as Sydney is no longer on the images.
Tony G