John Battelle points to a piece (reg required) by Max Kalehoff noting the striking increase in traffic driven to Wikipedia from search engine queries.
A ranking of all Web sites based on the total volume of traffic received directly from search engines placed Wikipedia at 146 in June 2004. But in September 2004 it jumped in the ranking to 93; 71 in December 2004; and in March 2005, it was the 33rd most popular site in terms of visits received from search engines.
That means Wikipedia is impacting not only the trivial results of our Internet searches, but increasingly what content we consume and the types of answers we find to larger questions. This is a profound statement for anyone competing in the marketplace for attention to content and ideas.