Everyone knew it and now its official too. Google is the number 1 site on the Alexa Traffic ranking systems pushing Yahoo to second rank.
Google officialy dethroned Yahoo from the top spot on Jan 5 this year. However since then Yahoo managed to get back to top Spot on two days 10th and 17th (both weekends). This shift can be attributed to fall in number of unique visitors on Google on Weekends.
Youtube is on third while Live.com takes the fourth position.
The users who ues Alexa toolbar to monitor sites would only be able to see this change once Google beats Yahoo in the 3 month average rankings, which is the official ranking number displayed in toolbar and Alexa reports.
Also see: Alexa Rankings not updating