http://www.google.cn/logos/chongzhi09.gif

The doodle is related to Zu Chongzhi, a Chinese mathematician that found a good rational approximation for π (Zu Chongzhi π rate). He was born 1580 years ago.

http://en.wikipedia.org/wiki/Zu_Chongzhi

And the search string is:
http://www.google.cn/search?q=%E4%B8%96%E7%95%8C%E5%9C%B0%E7%90%83%E6%97%A5&hl=zh-CN&ct=earthday09&oi=ddle

No, that's for Earth Day.

You are right, it is from the clipboard when I tested Google.cn front page...

That Chongzhi search string is not known but no problem...