Google in Israel has issued a black out for the day; not shutting down but serving a black screen with white letters instead of an all white screen with black letters. The results pages however, are still in classic Google white.
In the US, Earth Hour will take place on March 29th at 8 pm, so look forward to perhaps Google.com being back in black on Satruday.
Last October Google went black in San Francisco to raise awareness for the Lights Out San Francisco campaign.
Funny that although Google has come out saying that blackening the Google screen does not save power, they have done so to boost awareness of energy conservation. Google cited a study and their positioning on blackening Google last year :
One idea, suggested by the site called “Blackle” (which is not related to Google, by the way, though the site does use our custom search engine), is to reduce energy used by monitors by providing search with a black background. We applaud the spirit of the idea, but our own analysis as well as that of others shows that making the Google homepage black will not reduce energy consumption. To the contrary, on flat-panel monitors (already estimated to be 75% of the market), displaying black may actually increase energy usage. Detailed results from a new study confirm this.