Google's WANG is smaller than you think.
Google once said they had 10,000 servers.
Now *third parties* suggest they have 200,000 - 500,000 servers, because they're bigger now and the hype has increased accordingly.
Google does not disclose how many servers it has, I think it is because it would be a huge disappointment.
They serve say 300 million queries a day. And say 2-5 billion adverts. So lets say 5 billion impressions a day. Thats less than 60,000 a seconds. If say each server can deliver 10 a second (in reality its 100-500), then thats 6000 server on general load.
A quick sanity check, say 30 data centres take the bulk of the load, that would be 200 servers per data centre or say 20 racks. About a floors worth of servers, which is what their NY center is, one floors worth of servers.
That number already has a 10-1 safety factor built into it.
Basically servers got a lot faster, and the exaggerated numbers got a lot bigger. I would put their servers at less than 10,000 now.