Back in high school I had a teacher who made it quite clear that Wikipedia should NEVER be cited as a source in ANY paper we were to hand in. Any other website was fair game, be it Encarta (remember THAT??), Britannica, or some random website a 12-year-old created.
Granted, that teacher's stance might have been hard, but it nevertheless taught us a valuable lesson: don't cite Wikipedia.
Especially when he's not the only one who doesn't appreciate it. A Philippino judge recently ruled against the government in a case where the govt relied on Wikipedia to support their case.