The above are all excellent posts and I agree with most of the points raised therein.
Question for discussion: what about restricted references? By this I mean journal articles for which one needs a subscription, or books? Suppose I get into a flame war over the specifics of the Robinson annealation (yeah, I don't see it happening either, but run with it). I can think of maybe one site other than Wikipedia which discusses this, so my options are run to a journal article by Dr. Robinson, or my fat textbook by Prof. Clayden (et al). I think it's reasonable to suggest most posters here don't have subscriptions to many or most journals.
On the subject - Wikipedia. Discuss.