Their search engine is being constantly improved every day by people using it. Every search result you click on is recorded, along with no doubt the time elapse

Their search engine is being constantly improved every day by people using it. Every search result you click on is recorded, along with no doubt the time elapsed before you clicked another result and so on until you found what you were looking for. Google is a gigantic statistics engine with a growing data set. And in terms of Google employees testing their search results - 1) their employees aren't exactly the average Google user demographic 2) their emplyees is way to small a number to draw any conclusions about how useful/accurate their search results are. They can only figure that out by trialing new algos on a fraction of users. If successful, they push to all.