Wikipedia - dumping ground for speculation

Do you allow your students to use sites such as WikiPedia (or other slightly moronic -pedia sites) as references in their work? I try and deter them but they still sneak through, did you know that a WIKI is an open access/anyone can publish with little or often no moderation at all (I consider it a forerunner to web-logs), you can read more on the Wiki.org website. We are always advising our students to take extra care to find credible sources when searching on the Internet, sites such as these have to be taken with a large pinch of salt.
To see what I mean, see the illustration included here (click the image to see a larger version) which was kindly provided by Mandy Morrell after she changed the sites entry for someone purportedly to have worked on the relational database model along with Fred Flintstone!
It's a shame that the WikiPedia doesn't have some kind of voting system to allow readers to vote as to the correctness of an entry, there are of course many valid entries on this site but Mandy's example just goes to show that perhaps if you use it you should cross-reference with another source first?