Jon Mitchell from Read Write Web did a nice article on how Google search really works.
Taken from the article :
Last week, I talked to Google Search lead designer Jon Wiley about the process of designing Google's iconic interface. What goes on behind that white box? For the second part of my interview series with the people who make Google Search, I talked to Google Fellow Ben Gomes. He's one of the elite engineers addressing the never-ending array of challenges we users pose by asking ever-more-complicated questions of Google.
The first time I spoke to Ben, he was introducing me to a brand new Google concept called Search, plus Your World. This time, we were able to delve much deeper into the fundamentals of Web search. Computing power at Google's scale is awesome to behold, and I asked Ben to take us along for a search query's ride one step at a time.