Maybe not news, considering our traffic rankings.... but this is one of the first "real" studies of Wikipedia use I've seen, conducted by the prestigious Pew Internet project and released in April 2007 in a "data memo". http://www.pewinternet.org/pdfs/PIP_Wikipedia07.pdf

The first few paragraphs: " More than a third of American adult internet users (36%) consult the citizen-generated online encyclopedia Wikipedia, according to a new nationwide survey by the Pew Internet & American Life Project. And on a typical day in the winter of 2007, 8% of online Americans consulted Wikipedia.

There has been ongoing controversy about the reliability of articles on Wikipedia. Still, the Pew Internet Project survey shows that Wikipedia is far more popular among the well-educated than it is among those with lower levels of education. For instance, 50% of those with at least a college degree consult the site, compared with 22% of those with a high school diploma.

And 46% of those age 18 and older who are current full- or part-time students have used Wikipedia, compared with 36% of the overall internet population. In addition, young adults and broadband users have been among those who are earlier adopters of Wikipedia. While 44% of those ages 18-29 use Wikipedia to look for information, just 29% of users age 50 and older consult the site. In a similar split, 42% of home broadband users look for information on Wikipedia, while just 26% of home dial-up users do so."