You may have already heard about Middlebury College's new policy restricting use of Wikipedia as a source for student papers, but this New York Times story is worth a read because it goes deeper than previous reports.
My academic department, probably like most, has its share of Wikipedia champions and Wikipedia detractors. I'm in the middle, at least for now. I use the site on occasion, but with an increasingly skeptical eye.
In class, I tell my editing students that when checking facts, Wikipedia is OK as a starting point in a search, but it must not be the last stop. (The list of original sources at the end of an entry can be a good trailhead.) But as I see more errors — not just factual, but also grammatical — on Wikipedia, I wonder whether I should follow Middlebury's lead and forbid any use of the site in the classroom.
While forbidding the use of Wikipedia seems a bit unrealistic to me (it is a resource, after all -- just not a very good one), the argument that students shouldn't be citing any encyclopedia as a reference seems as if it would serve your purpose: to promote the cause of fact checking and cross-checking. Ultimately, banning the use of Wikipedia is probably less likely to encourage students to realise the site's many shortcomings than is allowing them to research at Wikipedia, then (potentially) to find that information discredited by other, more reliable sources.