No one knows the exact number. You can refer to this page : http://www.datacenterknowledge.com/archives/2008/03/27/google-data-center-faq/ Here is the video of their latest Google Data Centers : http://www.youtube.com/watch?v=zRwPSFpLX8I - Dynashox -
It has 36 Data Centers across the world. With 150 racks per data center, that would mean Google has more than 200,000 servers.
Are u sure about it...from where u got it ?.. I got this count from net search but not from google site....