My own Wikipedia use is probably fairly similar to that identified by Head and Eisenberg amongst college students in the US. I do not get much use from Wikipedia in studying Librarianship or Information Literacy, but I would often turn to it during my undergraduate degree in English Literature to obtain "a summary about a topic [...] in addition to a small set of other commonly used information resources at the beginning of the research process". These days, I prefer to begin my information search using the recommended reading lists provided by the iSchool, but I may still rely on Wikipedia for providing a concise and (usually) up-to-date background on an unfamiliar subject.
I am more inclined to use Wikipedia outside of academic work, for looking up information on books, authors, musicians, or films (although I used to rely on sites like IMDb and AllMusic.) Perhaps unsurprisingly, articles on "Culture and Arts" make up almost a third of Wikipedia's content:
|Wikipedia content by subject as of January 2008|
Fair usage rights are detailed at Wikimedia Commons
* Head, A.J.; Eisenberg, M.B. (2010) 'How today’s college students use Wikipedia for course–related research'. First Monday, 15 (3).