Wikimedia’s Leuksman.com has published some traffic and referral information on the Wikimedia project, majority of which is Wikipedia. The numbers are based upon small samples, but show some amazing information.
For example, Wikimedia attracts 7 billion page views per month and Google refers 24% of its traffic. The only larger referral for traffic is internal links within the Wikimedia network. Meaning Google sends Wikimedia almost 1.7 billion referrals a month.
Yahoo follows Google in referring 2% of Wikimedia’s traffic, with MSN & Live combining for roughly .6% and Ask.com sending .05%.
For more information on the traffic and referrer breakdown, visit Wikimedia page views @ leuksman.com.