Let start by saying (again) that I do like Wikipedia. But (and here we go) I don't think people really know how to "use" it. And I don't mean, they don't know how to look up specific articles in it, or modify things in it, etc. I mean, people don't know how to treat it as an information source. The common complaint about it is that it's not "authoritative" like the Encyclopedia Britannica (the usual comparison). And then the retort to that is, "Well the Encyclopedia Britannica makes mistakes too!" I hate that. First of all, let's try to get along people, ok?
Second of all, that dismisses the whole value of both sources, particularly Wikipedia. And it shows a fundamental misunderstanding about what Wikipedia is, or rather, what it does for us. Take as an example, how people usually refer to information they find in Wikipedia. I'm reading along in the 2006-07 Annual Report for the Canadian Cochrane Network and Centre (the Canadian part of the Cochrane Collaboration, an organization successfully high quality, timely, and most importantly as near-certain as possible, health care evidence materials... read the first few pages of the report) and they refer to a description of Cochrane found in Wikipedia by saying "Wikipedia, the popular online community encyclopaedia states..." it. This is the common mistake. Wikipedia did not state it. A user of Wikipedia stated it. You may think, "Well, duh!", but this is an important distinction. Encyclopedia Britannica (the organization) is an entity that has taken on the responsibility for the information put forth in the Encyclopedia Britannica (the information source). Wikipedia has not. They can't. All they've done is provide a forum in which anyone can manipulate text, that happens to be in the form of an encyclopedia. I'm not saying that this makes it less truthly or trustworthy or authoritative, just that when you citing something in Wikipedia, the author isn't Wikipedia. It's "Chrismoore123" or "Thinboy00" or "Noodlenozzle", the user that typed it in. They're responsible. They're the source that you're judging authoritative or not. Individuals created the entries in Encyclopedia Britannica too, but Encyclopedia Britannica (the organization) has taken efforts to make sure those individuals are qualified and us readers trust them on that, or at least hold them responsible for their efforts.
One interesting difference is how time plays into judging the authority of these two sources. In Encyclopedia Britannica, we assume that the newer the information is, the better, the more accurate it is. Although in Wikipedia we do this to some extent too, it should also be seen that in a community where anyone and everyone can change anything and everything, the older the content is, that is the longer it's stayed around without anyone changing it, the better (or at least, most agreed upon) it probably is as well.