In the SEO field, nothing is for sure

However, Alexa gives a rough estimate of a website's popularity.
According to Alexa, Yahoo! is the world's highest traffic website, so it may mean that people should be using Yahoo! search more than Google. But this is not the case with Google taking a very large chunk of the search market share.
I don't believe Google gives any consideration to Alexa rank. But just like everything else, other than a "few boys and girls @ Google" nobody knows for sure. Personally, I don't see any reason in believing in any of these stats
