[See also this more detailed post.]
There are all kinds of uses for Wikipedia. Because Wikipedia is open to input from anyone who is interested in a subject, you sometimes find little nuggets of specialized information that you would not get (as easily) elsewhere. Its "neutral point of view" policy also often ensures that arguments on both sides of controversies are presented (sometimes in a somewhat artificially "balanced" manner). A good article really can teach you something about the subject matter.
Wikipedia is also a reasonably dependable source of reliable sources of information. That is, it often cites perfectly good sources. But it is not itself a reliable source of information.
Much of its unique value comes from its open and dynamic platform, which is also what makes it a poor source of authoritative knowledge. Wikipedia is "the encyclopedia that anyone can edit" and many of its articles change several times a day. So it is of little use to the reader to know that Wikipedia makes a particular claim about an event, or that Wikipedia defines a certain concept in a particular way.
It does not help to specifiy the date you read the article, or to cite the particular version of the article you're quoting from. Either way, you would have to have some special reason to believe that this version of the article is right. And if you have such a reason then you also have a better source for the point in question. Cite that source, not Wikipedia.