It seems that they have been working on this for a long time, as you can see in this video that they've put up in March: http://www.youtube.com/watch?v=hPhFc6GqVdU#t=97s

I think it's really interesting to see what huge amounts of time goes into these redesigns at a company like Google. It's very different from what I do.

It's also interesting to see how the design has evolved from what they showed in March to what they finally arrived at.