The information is usually correct, though as I think somebody may have stated it can often be presented in a slightly biased way. Not that articles from experts aren't entirely unbiased or anything but usually if you want to quote an article in an important essay or something, you'd usually want to find something as close to the original source as possible. Wikipedia certainly isn't that.
And yes, I have seen it be wrong when I was looking up something regarding a maths assignment (it was a case of them having the all of the actual steps right but not understanding the reasoning behind a couple of them, my mate sorted that out though).
And yes, I have seen it be wrong when I was looking up something regarding a maths assignment (it was a case of them having the all of the actual steps right but not understanding the reasoning behind a couple of them, my mate sorted that out though).