CNet has published an interesting information about Google data center and estimates that they have 2,00,000 servers spanned across 36 data centers across the globe. From the article:
On the other hand, Dean seemingly thinks clusters of 1,800 servers are pretty routine, if not exactly ho-hum. And the software company runs on top of that hardware, enabling a sub-half-second response to an ordinary Google search query that involves 700 to 1,000 servers, is another matter altogether.
Google doesn't reveal exactly how many servers it has, but I'd estimate it's easily in the hundreds of thousands. It puts 40 servers in each rack, Dean said, and by one reckoning, Google has 36 data centers across the globe. With 150 racks per data center, that would mean Google has more than 200,000 servers, and I'd guess it's far beyond that and growing every day.
Sounds like a great place to work :)