I received this one paper to review for an economic journal. I returned it to the Editor with notes for the author, among which was "please do not rely your argument(s) on reference like Wikipedia". Of course if the argument were sound and flawless, I wouldn't even care whether he cited something or not. But it was not sound and it was flawed, I think. No, I have nothing personal against Wikipedia. In fact, I think, it is a very useful resource for curious people like you and me.
But, not as a key reference for an academic paper. Wikipedia is a good place to find facts, numbers, etc. It is even a useful place where you can be directed to reference somewhere else that is more credible. But, it is not by and in itself a reference. Basing an argument on what posted in Wikipedia itself is shaky, since everybody can change or add entry to the post any time. It is in fact designed to work that way, i.e. open encyclopedia. It is true that any false entries (or even vandalism) will eventually get corrected by those who care about the given post, but you never know if what you take from it is already the correct(ed) one or not.
(Of course blogs suffer the same thing. Blogs are for fun, not for academic citation).
By the way, this reminds me of an event organized by students last month. I was asked to participate in an academic writing workshop. The authors, they also seemed to like Wikipedia so much. But there was one case that's even worse. The author was writing a paper on labor market. She used not only Wikipedia as her main reference, but also some ... motivational books. Not that motivational books or chicken soups et cetera are bad, but for an academic paper? Yes, I get motivated when I read some fancy novels, but at least I kept them out of my papers (except maybe when I am writing literary criticism which may never happen).