I read an interesting article the other day in which they interviewed one of the chief IT people at Google and a point was made which I hadn't really considered. They were talking about managing the cluster of servers that is Google, and how much work it must be. This IT person went on to say that they had developed their own custom patch management system in house to manage the changes required to their software.
That got me to thinking. Estimates have put the Google cluster at anywhere between 10,000 and 80,000 servers, working in tandem, to ultimately produce that search box you see when you go to Google.com.