A friend of mine who is a university prof told his students they could not cite Wikipedia in their references. Partly because he considers it lazy research and partly because he discovered how many citations on Wikipedia were actually circular. That is to say a reference on Wikipedia cited another document as a source and if you followed that document's citations and so on you eventually got back to the original page on Wikipedia.
Also have you ever noticed how many pages there are out there where the text is identical to that on Wikipedia? Often it's lazy people creating pages and just lifting the content wholesale. Sometimes, however, it is Wikipedia "editors" lifting their content wholesale.
Now I'm sure ol' Jimmy had the noblest of intentions when he set up his wiki, but some editors clearly do not. There those who mess about with entries for the lulz, that was something that was always going to happen. There are those who will screw with entries because they happen to have a personal interest. PR companies are a favourite for this and again it's something Wales and his team have to deal with. But people lifting content wholesale is something I just don't understand. Plagiarism to get a better mark on a paper? I can see what that might happen. Plagiarism for financial gain? Again I can see why somebody might resort to that. But plagiarism for no gain whatsoever? Nope I just don't get it.
The problem of circular references, however, is something that Wikipedia really need to deal with. Not only do they need to be weeded out, but the content that uses them as justification needs to be called into question.