In short, yes. It is. But, but, everyone says it isn't accurate and should never be used as a source. Yes, everyone does say that. Here's why they're wrong:
Wikipedia was studied by the journal Nature and found to be about as accurate as the Encyclopedia Britannica. If you have experience in researching and disseminating information, you may know that Encyclopedia Britannica is well-respected for its information, but it has as many errors as most other respected sources. Actually, I've seen errors in Nature before as well. You have to expect a certain margin of error, no matter what resource you use.
The publisher of Encyclopedia Britannica admitted on NPR that his publication and Wikipedia have about the same accuracy. Of course, he is now debating the findings in the press. And, that's fine. The test appeared to be a fair study, consisting of a blind comparison of 50 articles from each publication.
I do use Wikipedia as a starting point, and I do think that people who are afraid to read it for fear of inaccuracies are inexperienced writers who don't really understand the dissemination process. I had four years of strenuous training as a journalist, so I don't just look at any fact and assume that it's true. If I can find a fact and then find it backed up somewhere that I trust, then that's a good fact. One of the best things about Wikipedia is that it requires extensive citations. For any piece of information that does not include a citation, there will be a notation mentioning it.
That means that anyone using Wikipedia as a reference can simply look at the referenced material and gauge it's accuracy. The references will be listed at the bottom of each page, and I know that many writers do use those references in their works.
Now, being a writer with a journalistic mind, I did set out to test the site to see how quickly something inaccurate would be cleaned up. About a year ago, I chose a Wikipedia page and edited it, adding in a long diatribe of mostly my opinion on the topic. I did use some fact, which was from a book that I read years ago, but did not cite specific passages or pages. Within hours I received a message thanking me for "experimenting" with the site, but that what I wrote had to be removed. Will most websites do this, or even check their information to make sure that it's accurate? If you're a web writer, you already know the answer to that.
So, why the hysteria about never using Wikipedia? I think a lot of it has to do with writers and editors who haven't read the study and haven't investigated the site to see how accurate it is. Many of them don't understand that disseminating information is just as important as finding it. I have a major client who does not allow Wikipedia to be used at all as a source. They will, however, allow me to use AC as a reference, despite there being no editing to AC stories, and most of the work there being based on opinion and with no citation whatsoever. For that same client, I have been able to use blogs, a forum post and other assorted pages as sources, but never Wikipedia. Why?
Is there a chance that a fact you read on Wikipedia isn't accurate? Certainly. That's what the citations are for. If you don't see a fact backed up, don't use it. But, if you read the first article that I referenced above, you may have seen this quote about the EB, "the longer established encyclopaedia does not claim to be error free." And it's correct- no work, not newspapers, magazines, websites or encyclopedias, claim to be completely free of errors. How many times have you seen something inaccurate in your local newspaper or in a magazine story? It happens.
The key for writers is to disseminate the information the best they can, and never to trust just one source for anything. Wikipedia is a good starting point, just like any other source you run across. The forum post that I mentioned using as a reference? It was about an extremely obscure subject about which little was available on the web. I checked out the writer of the post and looked at her website thoroughly to establish that she actually new what she was talking about. If you're a professional, you will always make sure that what you use as materials is as accurate as possible.
Any source, whether it's Wikipedia, the EB, blogs or anything else should always, always be corroborated by a second source. It doesn't matter how respected the work is or how professional it sounds- if you can't back it up with something, it's too risky. If you can back it up, what does it matter where it originally came from?