From our French researcher, a student-based study of Yahoo and Google, with conclusions that I both agree with (Wikipedia is starting to dominate results) and don’t (general search engines have had their day):
The detailed examination of links returned is equally instructive. The first link offered by Google and Yahoo is identical in 27% of cases. In a previous study (using a slightly different protocol), conducted in December 2005, the proportion was 24%. The order of magnitude is thus similar.
The most surprising result came from the use of Wikipedia. This use was marginal in December 2005 (see study). At the time, for all 10 results on the first page, 2% of the links proposed by Google and 4% of those proposed by Yahoo came from Wikipedia. On the first link alone, Google offered no Wikipedia results (at least not in our sample) and Yahoo offered 7%.
The strategies have changed completely. Today 27% of Google’s results on the first link alone come from Wikipedia, as do 31 % of Yahoo’s.
How can this sudden interest in Wikipedia by both engines be explained? It is undoubtedly connected with the increasing difficultly engines have in calculating satisfactory ranking.