It's a energy saving search engine powered by -who else- Google. It's quite interesting, instead of white, this web use black colour for their pages. They said, with black, it's only use less power (about 59 watts) rather than white (about 74 watts for a display). So, if you concern about saving your environment, global warming etc (but especially to saving your own money - pay less for your electricity bill) yo may think to change your web page to black.
The unfortunate thing is: this is still limited. Means, only when you use Google black aka Blackle you will see the black screen. But if you click the web that you search from Blackle it still turns on white. Or others colors but black. Sorry, you can't save your money just yet.