Google stopped being a search engine (for me) at the latest on May 10, 2006:
What would you expect when you search for “credit card”?
Visa, MasterCard, Citibank, American Express, etc.
Not Creditcards.com, credit.com, good-credit-card.com, credit-cards-x.blogspot.com
Of course Google had been manipulating the search results for much longer (e.g. the “miserable failure” fiasco), but this was the first time that they declared that such manipulation was actually their modus operandi.